Negative electrodes for electrochemical cells

ABSTRACT

Various embodiments provide a battery, a bulk energy storage system including the battery, and/or a method of operating the bulk energy storage system including the battery. In various embodiment, the battery may include a first electrode, an electrolyte, and a second electrode, wherein one or both of the first electrode and the second electrode comprises direct reduced iron (“DRI”). In various embodiments, the DRI may be in the form of pellets. In various embodiments, the pellets may comprise at least about 60 wt % iron by elemental mass, based on the total mass of the pellets. In various embodiments, one or both of the first electrode and the second electrode comprises from about 60% to about 90% iron and from about 1% to about 40% of a component comprising one or more of the materials selected from the group of SiO 2 , Al 2 O 3 , MgO, CaO, and TiO 2 .

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/711,253 entitled “Negative Electrodes forMetal-Air Batteries” filed Jul. 27, 2018, U.S. Provisional ApplicationNo. 62/790,668 entitled “Negative Electrodes for Metal-Air Batteries”filed Jan. 10, 2019, and U.S. Provisional Patent Application No.62/868,511 entitled “Negative Electrodes for Metal-Air Batteries” filedJun. 28, 2019. The entire contents of all three applications are herebyincorporated by reference for all purposes.

BACKGROUND

Energy storage technologies are playing an increasingly important rolein electric power grids; at a most basic level, these energy storageassets provide smoothing to better match generation and demand on agrid. The services performed by energy storage devices are beneficial toelectric power grids across multiple time scales, from milliseconds toyears. Today, energy storage technologies exist that can supporttimescales from milliseconds to hours, but there is a need for long andultra-long duration (collectively, ≥8 h) energy storage systems.

This Background section is intended to introduce various aspects of theart, which may be associated with embodiments of the present inventions.Thus, the foregoing discussion in this section provides a framework forbetter understanding the present inventions, and is not to be viewed asan admission of prior art.

SUMMARY

Materials, designs, and methods of fabrication for metal electrodes forelectrochemical cells are disclosed. In various embodiments, thenegative electrode comprises metallic pellets arranged in one or more,configurations, including multiple layers.

In various embodiments, pellets may comprise one or more forms of iron,ranging from highly reduced (more metallic) iron to highly oxidized(more ionic) iron. In various embodiments, the pellets may includevarious iron compounds, such as iron oxides, hydroxides, sulfides, orcombinations thereof. In various embodiments, the pellets may includeone or more secondary phases, such as silica (SiO₂) or silicates,calcium oxide (CaO), magnesium oxide (MgO), etc.

In various embodiments, pellets may be sintered iron agglomerates withvarious different shapes. In various embodiments, sintered ironagglomerate pellets may be formed in a furnace, such as a continuousfeed calcining furnace, batch feed calcining furnace, shaft furnace,rotary calciner, rotary hearth, etc. In various embodiments, pellets maycomprise forms of reduced and/or sintered iron-bearing precursors knownto those skilled in the art as direct reduced iron (DRI), and/or itsbyproduct materials. Various embodiments may include processing pellets,including DRI pellets, using mechanical, chemical, and/or thermalprocesses before introducing the pellets into the electrochemical cell.

In various embodiments, the negative electrode may be a composite metalelectrode comprised of a mixture of spherical or substantially sphericalmetallic pellets and powdered metal feedstock. In various embodiments,the powdered metal feedstock may be wetted by electrolyte. In variousembodiments, the negative electrode may be comprised of a mixture ofiron ore (e.g., taconite, etc.) pellets and conductive DRI fines, spongeiron, and/or atomized iron. “DRI fines” are understood to meanparticulates smaller in size than the DRI pellets but which are producedconcurrently with the DRI pellets, or particulates produced from DRIpellets by comminution, handling, or thermal or chemical means.

In various embodiments, the negative electrode may include the pellets,which may be grouped in an ordered array. In various embodiments, thepellets may be arranged packed in a bed such that macro-pores arecreated between two or more pellets in contact with one another. Invarious embodiments, the pellets may each include micro-pores. Invarious embodiments, electrolyte may fill the micro-pores ormacro-pores, or be flowed through the pore space surrounding the pelletscomprising the electrode.

In various embodiments, a layer of powdered iron may form an interfacebetween the pellets of the negative electrode and a current collectorwherein the negative electrode further comprises a layer of powderediron configured to form an interface between the pellets and a currentcollector of the electrochemical cell.

Various embodiments may include systems and methods for monitoring thestate-of-charge of the negative electrode comprising metallic pelletsarranged in one or more layers.

In various embodiments, the pellets may be synthesized in a first stageof a dual use energy storage plant and used in the negative electrode ina second stage of the dual use energy storage plant.

Various embodiments may provide a battery, including a first electrode;an electrolyte; and a second electrode, wherein one or both of the firstelectrode and the second electrode comprises direct reduced iron(“DRI”). In various embodiments, the DRI is in the form of pellets. Invarious embodiments, the pellets comprise at least about 60 wt % iron byelemental mass, based on the total mass of the pellets. In variousembodiments, the pellets comprise at least about 60 wt % metallic ironbased on the total mass of the pellets, the pellets have an averageparticle size of 4 mm to 20 mm, and the pellets comprise at least 60percent of the total mass of at least one of the first electrode and thesecond electrode. In various embodiments, the pellets comprise at leastabout 80 wt % metallic iron based on the total mass of the pellets. Invarious embodiments, the pellets comprise between about 90 wt % andabout 98 wt % metallic iron, based on the total mass of the pellets. Invarious embodiments, the pellets are spherical, rod-shaped, disk-shaped,plate shaped, briquette-shaped, or a combination thereof. In variousembodiments, the pellets are briquette-shaped and comprise hotbriquetted iron. In various embodiments, the hot briquetted iron isformed from powdered iron fines or iron pellets. In various embodiments,the pellets have an average length ranging from about 10 mm to about 500mm, an average width ranging from about 5 mm to about 250 mm, and anaverage height ranging from about 5 mm to about 200 mm. In variousembodiments, the DRI comprises iron ore, direct reduced grade iron ore,reduced taconite, wustite, magnetite, hematite, cementite, iron oxide,or any combination thereof. In various embodiments, the DRI comprisesDRI fines or powder. In various embodiments, the pellets have an averageinternal porosity ranging from about 10% to about 90% by volume. Invarious embodiments, the pellets have an average specific surface arearanging from about 0.19 m²/g to about 18 m²/g. In various embodiments,the pellets have a volume weighted mean pore size ranging from 1 to 10microns. In various embodiments, at least one of the first electrode andthe second electrode has a thickness of greater than 0.1 cm. In variousembodiments, the pellets are spherical and have an average diameterranging from about 0.5 mm to about 10 cm. In various embodiments, thepellets comprise greater than 0.5 wt % percent silica containingcompounds, based on the total weight of the pellets. In variousembodiments, the pellets comprise from about 1 wt % to about 5 wt %silica containing compounds by elemental mass, based on the total massof the pellets. In various embodiments, the pellets comprise from about1 wt % to about 25 wt % silica containing compounds by elemental mass,based on the total mass of the pellets. In various embodiments, apacking fraction of the pellets in at least one of the first electrodeand the second electrode is between 30% and 74%. In various embodiments,the pellets comprise: a primary phase comprising iron; and a secondaryphase comprising silicon or another metal. In various embodiments, thepellets comprise: a primary phase comprising iron; and a secondary phasecomprising cementite. In various embodiments, the secondary phasecomprises silica or a silicate. In various embodiments, the secondaryphase comprises titanium, vanadium, manganese, magnesium, calcium,phosphorus, carbon, aluminum, zirconium, or any combinations thereof. Invarious embodiments, at least one of the first electrode and the secondelectrode comprises a single layer of the pellets or multiple layers ofthe pellets. In various embodiments, the electrolyte is infiltratedbetween the pellets. In various embodiments, the battery may furtherinclude a current collector electrically connected to the pellets. Invarious embodiments, the current collector contacts a lower surface ofat least one of the first electrode and the second electrode, sidesurfaces of at least one of the first electrode and the secondelectrode, extends through at least one of the first electrode and thesecond electrode, or any combination thereof. In various embodiments,the pellets are sintered iron agglomerate pellets. In variousembodiments, the sintered iron agglomerate pellets are fabricated usinga continuous feed calcining furnace, a batch calcining furnace, a shaftfurnace, or any other type of furnace. In various embodiments, thesecond electrode may comprise a slurry or a gel. In various embodiments,at least one of the first electrode and the second electrode is acomposite metal electrode comprising a mixture of the pellets and asmaller metal particle composition. In various embodiments, the smallermetal particle composition is a powdered metal feedstock. In variousembodiments, the powdered metal feedstock is wetted by the electrolyte.In various embodiments, the smaller metal particle composition comprisesDRI fines, sponge iron, atomized iron, or any combination thereof. Invarious embodiments, the pellets comprise DR taconite. In variousembodiments, the pellets are synthesized in a first stage of operationin a dual use energy storage plant comprising the battery and loadedinto at least one of the first electrode and the second electrode in asecond stage of operation of the dual use energy storage plant. Invarious embodiments, the pellets are packed in a bed such thatmacro-pores are created between two or more pellets in contact with oneanother; and the pellets each include micro-pores in at least theirrespective outer surfaces. In various embodiments, the pellets are fusedtogether. In various embodiments, the pellets are pre-processedchemically, mechanically, thermally, electrically, and/orelectrochemically to fuse at least a portion of the pellets into apacked in a bed. In various embodiments, the battery may further includea pump configured to flow the liquid electrolyte over the pellets in thepacked bed. In various embodiments, the pellets each include micro-poresin their respective outer surfaces. In various embodiments, the pelletscomprise pores created by soaking the pellets in an etching bath beforeinstallation in at least one of the first electrode and the secondelectrode. In various embodiments, the etching bath is an acid bath. Invarious embodiments, at least one of the first electrode and the secondelectrode further comprises additive pellets comprising Bi₂O₃ or a metalsulfide. In various embodiments, the additive pellets comprise FeS,FeS², Na₂S, or a combination thereof. In various embodiments, thepellets are sintered iron pellets comprised of crushed direct reducediron (“DRI”) precursors and/or DRI fines. In various embodiments, thepellets are mechanically, chemically, electrically, electrochemically,and/or thermally pre-processed before installation in at least one ofthe first electrode and the second electrode. In various embodiments,the pre-processing includes pre-charging the pellets. In variousembodiments, the pellets are initially comprised of at least a portionof cementite (Fe₃C) before operation of the battery. In variousembodiments, at least one of the first electrode and the secondelectrode further comprises a layer of powdered iron configured to forman interface between the pellets and a current collector of the battery.In various embodiments, the battery may further include a monitoringsystem configured to monitor the state-of-charge (SOC) and/orstate-of-health of at least one of the first electrode and the secondelectrode. In various embodiments, the monitoring system comprises oneor more sensor connected to a controller. In various embodiments, theone or more sensors is selected from the group consisting of a straingauge, a Mossbauer spectrometer, a CCD detector, an ultrasonictransducer, an ion sensing electrode, a thermocouple, and a gas sensor.In various embodiments, at least one of the first electrode and thesecond electrode is a composite metal electrode comprising a mixture ofthe pellets and a conductive material dispersed between individualpellets. In various embodiments, the conductive material comprises oneor more conductive fibers, one or more wires, one or more meshes, and/orone or more sheets. In various embodiments, the first electrode is anegative electrode and comprises the DRI. In various embodiments, thebattery may further include an additive delivery system configured toadd one or more additives to the electrolyte. In various embodiments,the additive delivery system delivers liquid additives or solidadditives. In various embodiments, the one or more additives include asalt. In various embodiments, the salt is a carbonate salt orpolysulfide salt. In various embodiments, the one or more additivesinclude a sulfur-based additive. In various embodiments, the one or moreadditives include a surfactant additive. In various embodiments, the oneor more additives are configured to mitigate self-discharge and/orsuppress the hydrogen evolution reaction (HER). In various embodiments,at least one of the first electrode and the second electrode is undercompressive force. In various embodiments, at least one of the firstelectrode and the second electrode comprises additional conductivematerial. In various embodiments, the additional conductive materialsurrounds the iron-containing pellets. In various embodiments, theadditional conductive material is a foil, sheet, screen, or wire.

Various embodiments may provide a method for operating an energy storageplant, including operating the energy storage plant to produce activematerials; and using the active materials in the energy storage plantfor long-duration energy storage. In various embodiments, the productionof the active materials uses renewable energy.

Various embodiments may provide a bulk energy storage system, includingone or more batteries, wherein at least one of the one or more batteriesincludes a first electrode, an electrolyte, and a second electrode,wherein one or both of the first electrode and the second electrodecomprises direct reduced iron (“DRI”). In various embodiments, at leastone of the first electrode and the second electrode comprising DRI is anegative electrode comprising direct reduced iron (“DRI”) pellets. Invarious embodiments, at least one of the first electrode and the secondelectrode further comprises additive pellets. In various embodiments,the additive pellets are comprised of FeS, FeS₂, Bi₂O₃, or a metalsulfide. In various embodiments, the DRI comprises sintered iron pelletscomprised of crushed direct reduced iron (“DRI”) precursors and/or DRIfines. In various embodiments, the DRI is comprised of direct reducediron (“DRI”) pellets that are mechanically, chemically, and/or thermallypre-processed before installation in at least one of the first electrodeand the second electrode. In various embodiments, the DRI comprises atleast about 60 wt % metallic iron based on the total mass of thepellets, the DRI comprises direct reduced iron pellets having an averagesize of 4 mm to 20 mm and the direct reduced iron pellets comprise atleast 60 percent of the total mass of at least one of the firstelectrode and the second electrode. In various embodiments, the bulkenergy storage system is a long duration energy storage (LODES) system.

Various embodiments may provide a long duration energy storage systemconfigured to hold an electrical charge for at least 24 hours, thesystem including a housing; a first electrode, the electrode comprising:from about 60% to about 90% iron; and, from about 1% to about 40% of acomponent comprising one or more of the materials selected from thegroup consisting of SiO₂, Al₂O₃, MgO, CaO, and TiO₂; a second electrode;and, an electrolyte. In various embodiments, the component may compriseabout 1.5% to about 7.5% SiO₂. In various embodiments, the component maycomprise about 0.3% to about 3% Al₂O₃. In various embodiments, thecomponent may comprise about 0.25% to about 2% MgO. In variousembodiments, the component may comprise about 0.75% to about 2.5% CaO.In various embodiments, the component may comprise about 0.25% to about1.5% TiO₂. In various embodiments, the component may comprise 1% to 10%SiO₂. In various embodiments, the component may comprise 0.2% to 5%Al₂O₃. In various embodiments, the component may comprise 0.1% to 10%MgO. In various embodiments, the component may comprise 0.9% to 10% CaO.In various embodiments, the component may comprise 0.05% to 5% TiO₂. Invarious embodiments, at least 50% of the iron is Fe⁰. In variousembodiments, at least 50% of the iron is metallic iron. In variousembodiments, at the iron comprises Fe⁰, Fe²⁺ and Fe³⁺. In variousembodiments, the storage system has a power rating of at least about 100MW, a rated duration of at least about 100 hours, and an energy ratingof at least about 2,000 MWh. In various embodiments, the storage issystem has a power rating from about 50 MW to about 500 MW, a ratedduration from about 25 hours to about 500 hours, and an energy rating ofabout 3,000 MWh to about 90,000 MWh.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 2A is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 2B is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure

FIG. 3A is a schematic of an example continuous feed calcining furnaceconfigured to form sintered agglomerate pellets according to variousembodiments of the present disclosure.

FIG. 3B is a process flow diagram of an embodiment method for formingsintered porous metal electrodes.

FIG. 3C is a block diagram of an embodiment system for forming sinteredporous metal electrodes.

FIG. 3D is a block diagram of an embodiment system for forming sinteredporous metal electrodes

FIG. 4 is a schematic of an electrochemical cell including a compositemetal electrode with spherical pellets and metal feedstock according tovarious embodiments of the present disclosure.

FIG. 5 is a process flow diagram illustrating an embodiment method foron-site synthesis of active materials for bulk energy storage systemsusing renewable over-production.

FIG. 6 is a schematic of the electrochemical cell of FIG. 1 showingexpanded views of the macro-pores and micro-pores according to variousembodiments of the present disclosure.

FIG. 7 is a schematic of one pellet of the electrochemical cell of FIG.1 according to various embodiments of the present disclosure.

FIG. 8A is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 8B is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 8C is a schematic of a series of fluid connected electrochemicalcells, according to various embodiments of the present disclosure.

FIG. 9 is a schematic of an electrochemical cell including a mix ofactive material and additive material pellets, according to variousembodiments of the present disclosure.

FIG. 10 is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 11 is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIGS. 12A-12F are schematic views of electrochemical cells, according tovarious embodiments of the present disclosure.

FIG. 13A is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 13B is a schematic of an electrochemical cell, according to variousembodiments of the present disclosure.

FIG. 14 is a schematic of a filtration device, according to variousembodiments of the present disclosure.

FIGS. 15-23 illustrate various example systems in which one or moreaspects of the various embodiments may be used as part of bulk energystorage systems.

FIGS. 24A-24D are graphs illustrating DRI electrode first cycledischarge specific capacity (mAh/g_(DRI)), discharge vs cycle number,coulombic efficiency, and a subsequent cycle discharge specific capacity(mAh/g_(DRI)), respectively.

DETAILED DESCRIPTION

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.References made to particular examples and implementations are forillustrative purposes and are not intended to limit the scope of theclaims. The following description of the embodiments of the invention isnot intended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Unless otherwise noted, the accompanying drawings are not drawn toscale.

As used herein, unless stated otherwise, room temperature is 25° C. And,standard temperature and pressure is 25° C. and 1 atmosphere. Unlessexpressly stated otherwise all tests, test results, physical properties,and values that are temperature dependent, pressure dependent, or both,are provided at standard ambient temperature and pressure.

Generally, the term “about” and the symbol “˜” as used herein unlessspecified otherwise is meant to encompass a variance or range of ±10%,the experimental or instrument error associated with obtaining thestated value, and preferably the larger of these.

As used herein unless specified otherwise, the recitation of ranges ofvalues herein is merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range.Unless otherwise indicated herein, each individual value within a rangeis incorporated into the specification as if it were individuallyrecited herein.

As used herein, unless specified otherwise the terms %, weight % andmass % are used interchangeably and refer to the weight of a firstcomponent as a percentage of the weight of the total, e.g., formulation,mixture, particle, pellet, material, structure or product. As usedherein, unless specified otherwise “volume %” and “% volume” and similarsuch terms refer to the volume of a first component as a percentage ofthe volume of the total, e.g., formulation, mixture, particle, pellet,material, structure or product.

The following examples are provided to illustrate various embodiments ofthe present systems and methods of the present inventions. Theseexamples are for illustrative purposes, may be prophetic, and should notbe viewed as limiting, and do not otherwise limit the scope of thepresent inventions.

It is noted that there is no requirement to provide or address thetheory underlying the novel and groundbreaking processes, materials,performance or other beneficial features and properties that are thesubject of, or associated with, embodiments of the present inventions.Nevertheless, various theories are provided in this specification tofurther advance the art in this area. The theories put forth in thisspecification, and unless expressly stated otherwise, in no way limit,restrict or narrow the scope of protection to be afforded the claimedinventions. These theories many not be required or practiced to utilizethe present inventions. It is further understood that the presentinventions may lead to new, and heretofore unknown theories to explainthe function-features of embodiments of the methods, articles,materials, devices and system of the present inventions; and such laterdeveloped theories shall not limit the scope of protection afforded thepresent inventions.

The various embodiments of systems, equipment, techniques, methods,activities and operations set forth in this specification may be usedfor various other activities and in other fields in addition to thoseset forth herein. Additionally, these embodiments, for example, may beused with: other equipment or activities that may be developed in thefuture; and, with existing equipment or activities which may bemodified, in-part, based on the teachings of this specification.Further, the various embodiments and examples set forth in thisspecification may be used with each other, in whole or in part, and indifferent and various combinations. Thus, the configurations provided inthe various embodiments of this specification may be used with eachother. For example, the components of an embodiment having A, A′ and Band the components of an embodiment having A″, C and D can be used witheach other in various combination, e.g., A, C, D, and A. A″ C and D,etc., in accordance with the teaching of this Specification. Thus, thescope of protection afforded the present inventions should not belimited to a particular embodiment, configuration or arrangement that isset forth in a particular embodiment, example, or in an embodiment in aparticular figure.

As used herein, unless specified otherwise, the terms specific gravity,which is also called apparent density, should be given their broadestpossible meanings, and generally mean weight per unit volume of astructure, e.g., volumetric shape of material. This property wouldinclude internal porosity of a particle as part of its volume. It can bemeasured with a low viscosity fluid that wets the particle surface,among other techniques.

As used herein, unless specified otherwise, the terms actual density,which may also be called true density, should be given their broadestpossible meanings, and general mean weight per unit volume of amaterial, when there are no voids present in that material. Thismeasurement and property essentially eliminates any internal porosityfrom the material, e.g., it does not include any voids in the material.

Thus, a collection of porous foam balls (e.g., Nerf® balls) can be usedto illustrate the relationship between the three density properties. Theweight of the balls filling a container would be the bulk density forthe balls:

${{Bulk}\mspace{14mu}{Density}} = \frac{{weight}\mspace{14mu}{of}\mspace{14mu}{balls}}{{volume}\mspace{14mu}{of}\mspace{14mu}{container}\mspace{14mu}{filled}}$

The weight of a single ball per the ball's spherical volume would be itsapparent density:

${{Apparent}\mspace{14mu}{Density}} = \frac{{weight}\mspace{14mu}{of}\mspace{14mu}{one}\mspace{14mu}{ball}}{{volume}\mspace{14mu}{of}\mspace{14mu}{that}\mspace{14mu}{ball}}$

The weight of the material making up the skeleton of the ball, i.e., theball with all void volume removed, per the remaining volume of thatmaterial would be the actual density:

${{Actual}\mspace{14mu}{Density}} = \frac{{weight}\mspace{14mu}{of}\mspace{14mu}{material}}{{volume}\mspace{14mu}{of}\mspace{14mu}{void}\mspace{14mu}{free}\mspace{14mu}{material}}$

Embodiments of the present invention include apparatus, systems, andmethods for long-duration, and ultra-long-duration, low-cost, energystorage. Herein, “long duration” and “ultra-long duration” and similarsuch terms, unless expressly stated otherwise, should be given theirbroadest possible meaning and include periods of energy storage of 8hours or longer, such as periods of energy storage of 8 hours, periodsof energy storage ranging from 8 hours to 20 hours, periods of energystorage of 20 hours, periods of energy storage ranging from 20 hours to24 hours, periods of energy storage of 24 hours, periods of energystorage ranging from 24 hours to a week, periods of energy storageranging from a week to a year (e.g., such as from several days toseveral weeks to several months), etc. and would include LODES systems.Further, the terms “long duration” and “ultra-long duration”, “energystorage cells” including “electrochemical cells”, and similar suchterms, unless expressly stated otherwise, should be given their broadestpossible interpretation; and include electrochemical cells that may beconfigured to store energy over time spans of days, weeks, or seasons.

In general, in an embodiment, the long duration energy storage cell canbe a long duration electrochemical cell. In general, this long durationelectrochemical cell can store electricity generated from an electricalgeneration system, when: (i) the power source or fuel for thatgeneration is available, abundant, inexpensive, and combinations andvariations of these; (ii) when the power requirements or electricalneeds of the electrical grid, customer or other user, are less than theamount of electricity generated by the electrical generation system, theprice paid for providing such power to the grid, customer or other user,is below an economically efficient point for the generation of suchpower (e.g., cost of generation exceeds market price for theelectricity), and combinations and variations of these; and (iii)combinations and variations of (i) and (ii) as well as other reasons.This electricity stored in the long duration electrochemical cell canthen be distributed to the grid, customer or other user, at times whenit is economical or otherwise needed. For example, the electrochemicalcells may be configured to store energy generated by solar cells duringthe summer months, when sunshine is plentiful and solar power generationexceeds power grid requirements, and discharge the stored energy duringthe winter months, when sunshine may be insufficient to satisfy powergrid requirements.

Various embodiments are discussed in relation to the use of directreduced iron (DRI) as a material a battery (or cell), as a component ofa battery (or cell) and combinations and variations of these. In variousembodiments, the DRI may be produced from, or may be, material which isobtained from the reduction of natural or processed iron ores, suchreduction being conducted without reaching the melting temperature ofiron. In various embodiments the iron ore may be taconite or magnetiteor hematite or goethite, etc. In various embodiments, the DRI may be inthe form of pellets, which may be spherical or substantially spherical.In various embodiments the DRI may be porous, containing open and/orclosed internal porosity. In various embodiments the DRI may comprisematerials that have been further processed by hot or cold briquetting.In various embodiments, the DRI may be produced by reducing iron orepellets to form a more metallic (more reduced, less highly oxidized)material, such as iron metal (Fe⁰), wustite (FeO), or a composite pelletcomprising iron metal and residual oxide phases. In various non-limitingembodiments, the DRI may be reduced iron ore taconite, direct reduced(“DR”) taconite, reduced “Blast Furnace (BF) Grade” pellets, reduced“Electric Arc Furnace (EAF)-Grade” pellets, “Cold Direct Reduced Iron(CDRI)” pellets, direct reduced iron (“DRI”) pellets, Hot BriquettedIron (HBI), or any combination thereof. In the iron and steelmakingindustry, DRI is sometimes referred to as “sponge iron;” this usage isparticularly common in India. Embodiments of iron materials, includingfor example embodiments of DRI materials, for use in various embodimentsdescribed herein, including as electrode materials, may have, one, morethan one, or all of the material properties as described in Table 1below. As used in the Specification, including Table 1, the followingterms, have the following meaning, unless expressly stated otherwise:“Specific surface area” means, the total surface area of a material perunit of mass, which includes the surface area of the pores in a porousstructure; “Carbon content” or “Carbon (wt %)” means the mass of totalcarbon as percent of total mass of DRI; “Cementite content” or“Cementite (wt %)” means the mass of Fe₃C as percent of total mass ofDRI; “Total Fe (wt %)” means the mass of total iron as percent of totalmass of DRI; “Metallic Fe (wt %)” means the mass of iron in the Fe⁰state as percent of total mass of DRI; and “Metallization” means themass of iron in the Fe⁰ state as percent of total iron mass. Weight andvolume percentages and apparent densities as used herein are understoodto exclude any electrolyte that has infiltrated porosity or fugitiveadditives within porosity unless otherwise stated.

TABLE 1 Material Property Embodiment Range Specific surface area*0.01-25 m²/g Actual density** 4.6-7.1 g/cc Apparent density*** 2.3-6.5g/cc Minimum d_(pore, 90% volume)**** 10 nm-50 μm Minimumd_(pore, 50% surface area)*****  1 nm-15 μm Total Fe (wt %)^(#) 65-95%Metallic Fe (wt %)^(##) 46-90% Metallization (%)^(###) 59-96% Carbon (wt%)^(####) 0-5% Fe²⁺ (wt %)^(#####) 1-9% Fe³⁺ (wt %)^($) 0.9-25%  SiO₂(wt %)^($$)  1-15% Ferrite (wt %, XRD)^($$$) 22-97% Wustite (FeO, wt %,XRD)^($$$$)  0-13% Goethite (FeOOH, wt %, XRD)^($$$$$)  0-23% Cementite(Fe₃C, wt %, XRD)⁺ <<80%

*Specific surface area preferably determined by theBrunauer-Emmett-Teller adsorption method (“BET”), and more preferably asthe BET is set forth in ISO 9277 (the entire disclosure of which isincorporated herein by reference); recognizing that other tests, such asmethylene blue (MB) staining, ethylene glycol monoethyl ether (EGME)adsorption, electrokinetic analysis of complex-ion adsorption and aProtein Retention (PR) method may be employed to provide results thatcan be correlated with BET results.

**Actual density preferably determined by helium (He) pycnometry, andmore preferably as is set forth in ISO 12154 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results. Actual density may also be referred to as “truedensity” or “skeletal density” in the art.

***Apparent density preferably determined by immersion in water, andmore preferably as is set forth in ISO 15968 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results. Porosity may be defined as the ratio of apparentdensity to actual density:

${Porosity} = \frac{{apparent}\mspace{14mu}{density}}{{actual}\mspace{14mu}{density}}$

****d_(pore, 90% volume) preferably determined by mercury (Hg) intrusionporosimetry, and more preferably as is set forth in ISO 15901-1 (theentire disclosure of which is incorporated herein by reference);recognizing that other tests, such as gas adsorption, may be employed toprovide results that can be correlated with Hg intrusion results.d_(pore, 90% volume) is the pore diameter above which 90% of the totalpore volume exists.

*****d_(pore, 50% surface area) preferably determined by mercury (Hg)intrusion porosimetry, and more preferably as is set forth in ISO15901-1 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests, such as gas adsorption, may beemployed to provide results that can be correlated with Hg intrusionresults. d_(pore, 50% surface area) is the pore diameter above which 50%of free surface area exists.

#Total Fe (wt %) preferably determined by dichromate titrimetry, andmore preferably as is set forth in ASTM E246-10 (the entire disclosureof which is incorporated herein by reference); recognizing that othertests, such as titrimetry after tin(II) chloride reduction, titrimetryafter titanium(III) chloride reduction, inductively coupled plasma (ICP)spectrometry, may be employed to provide results that can be correlatedwith dichromate titrimetry.

##Metallic Fe (wt %) preferably determined by iron(III) chloridetitrimetry, and more preferably as is set forth in ISO 16878 (the entiredisclosure of which is incorporated herein by reference); recognizingthat other tests, such as bromine-methanol titimetry, may be employed toprovide results that can be correlated with iron(III) chloridetitrimetry.

###Metallization (%) preferably determined by the ratio of metallic Feto total Fe, each as preferably determined by the methods previouslydescribed.

####Carbon (wt %) preferably determined by infrared absorption aftercombustion in an induction furnace, and more preferably as is set forthin ISO 9556 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests, such as various combustion andinert gas fusion techniques, such as are described in ASTM E1019-18 maybe employed to provide results that can be correlated with infraredabsorption after combustion in an induction furnace.

#####Fe²⁺ (wt %) preferably determined by titrimetry, and morepreferably as is set forth in ASTM D3872-05 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that othertests, such as Mossbauer spectroscopy, X-ray absorption spectroscopy,etc., may be employed to provide results that can be correlated withtitrimetry.

$ Fe³⁺ (wt %) preferably determined by the mass balance relation betweenand among Total Fe (wt %), Metallic Fe (wt %), Fe²⁺ (wt %) and Fe³⁺ (wt%). Specifically the equality Total Fe (wt %)=Metallic Fe (wt %)+Fe²⁺(wt %)+Fe³⁺ (wt %) must be true by conservation of mass, so Fe³⁺ (wt %)may be calculated as Fe³⁺ (wt %)=Total Fe (wt %)−Metallic Fe (wt %)−Fe²⁺(wt %).

$$ SiO₂ (wt %) preferably determined by gravimetric methods, and morepreferably as is set forth in ISO 2598-1 (the entire disclosure of whichis incorporated herein by reference); recognizing that other tests, suchas reduced molybdosilicate spectrophotometric methods, x-ray diffraction(XRD), may be employed to provide results that can be correlated withgravimetric methods. In certain methods, the SiO₂ wt % is not determineddirectly, but rather the Si concentration (inclusive of neutral andionic species) is measured, and the SiO₂ wt % is calculated assuming thestoichiometry of SiO₂; that is, a 1:2 molar ratio of Si:O is assumed.

$$$ Ferrite (wt %, XRD) preferably determined by x-ray diffraction(XRD).

$$$$ Wustite (FeO, wt %, XRD) preferably determined by x-ray diffraction(XRD).

$$$$$ Goethite (FeOOH, wt %, XRD) preferably determined by x-raydiffraction (XRD).

+ Cementite (Fe₃C, wt %, XRD) preferably determined by x-ray diffraction(XRD).

Additionally, embodiments of iron materials, including for exampleembodiments of DRI materials, for use in various embodiments describedherein, including as electrode materials, may have one or more of thefollowing properties, features or characteristics, (noting that valuesfrom one row or one column may be present with values in different rowsor columns) as set forth in Table 1A.

TABLE 1A Fe total (wt %)^(!) >60% >70%  >80% ~83-94%  SiO₂ (wt %)^(!!)<12% <7.5%     1-10%  1.5-7.5% Al₂O₃ (wt %)^(!!!) <10% <5% 0.2-5% 0.3-3%  MgO (wt %)^(!!!!) <10% <5% 0.1-10% 0.25-2%   CaO (wt %)^(!!!!!)<10% <5% 0.9-10% 0.75-2.5% TiO₂ (wt %)^(&) <10% <2.5%   0.05-5% 0.25-1.5% Size (largest <200 mm ~50 to ~150 mm ~2 to ~30 mm ~4 to ~20 mmcross-sectional distance, e.g. for a sphere the diameter) Actual Density~5 ~5.8 to ~6.2 ~4.0 to ~6.5 <7.8 (g/cm³)^(&&) Apparent <7.8 >5 >43.4~3.6 Density (g/cm³)^(&&&) Bulk Density <7 >1.5 ~2.4 to ~3.4 ~1.5 to~2.0 (kg/m³)^(&&&&) Porosity >15% >50%  ~20% to ~90% ~50% to ~70%(%)^(&&&&&)

! Total Fe (wt %) preferably determined by dichromate titrimetry, andmore preferably as is set forth in ASTM E246-10 (the entire disclosureof which is incorporated herein by reference); recognizing that othertests, such as titrimetry after tin(II) chloride reduction, titrimetryafter titanium(III) chloride reduction, inductively coupled plasma (ICP)spectrometry, may be employed to provide results that can be correlatedwith dichromate titrimetry.

!! SiO₂ (wt %) preferably determined by gravimetric methods, and morepreferably as is set forth in ISO 2598-1 (the entire disclosure of whichis incorporated herein by reference); recognizing that other tests, suchas reduced molybdosilicate spectrophotometric methods, x-ray diffraction(XRD), may be employed to provide results that can be correlated withgravimetric methods. In certain methods, the SiO₂ wt % is not determineddirectly, but rather the Si concentration (inclusive of neutral andionic species) is measured, and the SiO₂ wt % is calculated assuming thestoichiometry of SiO₂; that is, a 1:2 molar ratio of Si:O is assumed.

!!! Al₂O₃ (wt %) preferably determined by flame atomic absorptionspectrometric method, and more preferably as is set forth in ISO 4688-1(the entire disclosure of which is incorporated herein by reference);recognizing that other tests, such as x-ray diffraction (XRD), may beemployed to provide results that can be correlated with flame atomicabsorption spectrometric method. In certain methods, the Al₂O₃ wt % isnot determined directly, but rather the Al concentration (inclusive ofneutral and ionic species) is measured, and the Al₂O₃ wt % is calculatedassuming the stoichiometry of Al₂O₃; that is, a 2:3 molar ratio of Al:Ois assumed.

!!!! MgO (wt %) preferably determined by flame atomic absorptionspectrometric method, and more preferably as is set forth in ISO 10204(the entire disclosure of which is incorporated herein by reference);recognizing that other tests, such as x-ray diffraction (XRD), may beemployed to provide results that can be correlated with flame atomicabsorption spectrometric method. In certain methods, the MgO wt % is notdetermined directly, but rather the Mg concentration (inclusive ofneutral and ionic species) is measured, and the MgO wt % is calculatedassuming the stoichiometry of MgO; that is, a 1:1 molar ratio of Mg:O isassumed.

!!!!! CaO (wt %) preferably determined by flame atomic absorptionspectrometric method, and more preferably as is set forth in ISO 10203(the entire disclosure of which is incorporated herein by reference);recognizing that other tests, such as x-ray diffraction (XRD), may beemployed to provide results that can be correlated with flame atomicabsorption spectrometric method. In certain methods, the CaO wt % is notdetermined directly, but rather the Ca concentration (inclusive ofneutral and ionic species) is measured, and the CaO wt % is calculatedassuming the stoichiometry of CaO; that is, a 1:1 molar ratio of Ca:O isassumed.

& TiO₂ (wt %) preferably determined by a diantipyrylmethanespectrophotometric method, and more preferably as is set forth in ISO4691 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests, such as x-ray diffraction(XRD), may be employed to provide results that can be correlated withthe diantipyrylmethane spectrophotometric method. In certain methods,the TiO₂ wt % is not determined directly, but rather the Ticoncentration (inclusive of neutral and ionic species) is measured, andthe TiO₂ wt % is calculated assuming the stoichiometry of TiO₂; that is,a 1:2 molar ratio of Ti:O is assumed.

&& Actual density preferably determined by helium (He) pycnometry, andmore preferably as is set forth in ISO 12154 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results. Actual density may also be referred to as “truedensity” or “skeletal density” in the art.

&&& Apparent density preferably determined by immersion in water, andmore preferably as is set forth in ISO 15968 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results.

&&&& Bulk Density (kg/m³) preferably determined by measuring the mass ofa test portion introduced into a container of known volume until itssurface is level, and more preferably as is set forth in Method 2 of ISO3852 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests may be employed to provideresults that can be correlated with the massing method.

&&&&& Porosity determined preferably by the ratio of the apparentdensity to the actual density:

${Porosity} = \frac{{apparent}\mspace{14mu}{density}}{{actual}\mspace{14mu}{density}}$

The properties set forth in Table 1, may also be present in embodimentswith, in addition to, or instead of the properties in Table 1A. Greaterand lesser values for these properties may also be present in variousembodiments.

In embodiments the specific surface area for the pellets can be fromabout 0.05 m²/g to about 35 m²/g, from about 0.1 m²/g to about 5 m²/g,from about 0.5 m²/g to about 10 m²/g, from about 0.2 m²/g to about 5m²/g, from about 1 m²/g to about 5 m²/g, from about 1 m²/g to about 20m²/g, greater than about 1 m²/g, greater than about 2 m²/g, less thanabout 5 m²/g, less than about 15 m²/g, less than about 20 m²/g, andcombinations and variations of these, as well as greater and smallervalues.

In general, iron ore pellets are produced by crushing, grinding ormilling of iron ore to a fine powdery form, which is then concentratedby removing impurity phases (so called “gangue”) which are liberated bythe grinding operation. In general, as the ore is ground to finer(smaller) particle sizes, the purity of the resulting concentrate isincreased. The concentrate is then formed into a pellet by a pelletizingor balling process (using, for example, a drum or disk pelletizer). Ingeneral, greater energy input is required to produce higher purity orepellets. Iron ore pellets are commonly marketed or sold under twoprincipal categories: Blast Furnace (BF) grade pellets and DirectReduction (DR Grade) (also sometimes referred to as Electric Arc Furnace(EAF) Grade) with the principal distinction being the content of SiO₂and other impurity phases being higher in the BF grade pellets relativeto DR Grade pellets. Typical key specifications for a DR Grade pellet orfeedstock are a total Fe content by mass percentage in the range of63-69 wt % such as 67 wt % and a SiO₂ content by mass percentage of lessthan 3 wt % such as 1 wt %. Typical key specifications for a BF gradepellet or feedstock are a total Fe content by mass percentage in therange of 60-67 wt % such as 63 wt % and a SiO₂ content by masspercentage in the range of 2-8 wt % such as 4 wt %.

In certain embodiments the DRI may be produced by the reduction of a“Blast Furnace” pellet, in which case the resulting DRI may havematerial properties as described in Table 2 below. The use of reduced BFgrade DRI may be advantageous due to the lesser input energy required toproduce the pellet, which translates to a lower cost of the finishedmaterial.

TABLE 2 Material Property Embodiment Range Specific surface area*0.21-25 m²/g Actual density** 5.5-6.7 g/cc Apparent density*** 3.1-4.8g/cc Minimum d_(pore, 90% volume)**** 50 nm-50 μm Minimumd_(pore, 50% surface area)*****  1 nm-10 μm Total Fe (wt %)^(#)81.8-89.2% Metallic Fe (wt %)^(##) 68.7-83.2% Metallization (%)^(###)84-95% Carbon (wt %)^(####) 0.03-0.35% Fe²⁺ (wt %)^(#####)   2-8.7% Fe³⁺(wt %)^($) 0.9-5.2% SiO₂ (wt %)^($$) 3-7% Ferrite (wt %, XRD)^($$$)80-96% Wustite (FeO, wt %, XRD)^($$$$)  2-13% Goethite (FeOOH, wt %,XRD)^($$$$$)  0-11% Cementite (Fe₃C, wt %, XRD)⁺  0-80%

*Specific surface area preferably determined by theBrunauer-Emmett-Teller adsorption method (“BET”), and more preferably asthe BET is set forth in ISO 9277 (the entire disclosure of which isincorporated herein by reference); recognizing that other tests, such asmethylene blue (MB) staining, ethylene glycol monoethyl ether (EGME)adsorption, electrokinetic analysis of complex-ion adsorption and aProtein Retention (PR) method may be employed to provide results thatcan be correlated with BET results.

**Actual density preferably determined by helium (He) pycnometry, andmore preferably as is set forth in ISO 12154 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results. Actual density may also be referred to as “truedensity” or “skeletal density” in the art.

***Apparent density preferably determined by immersion in water, andmore preferably as is set forth in ISO 15968 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results. Porosity may be defined as the ratio of apparentdensity to actual density:

${Porosity} = \frac{{apparent}\mspace{14mu}{density}}{{actual}\mspace{14mu}{density}}$

****d_(pore, 90% volume) preferably determined by mercury (Hg) intrusionporosimetry, and more preferably as is set forth in ISO 15901-1 (theentire disclosure of which is incorporated herein by reference);recognizing that other tests, such as gas adsorption, may be employed toprovide results that can be correlated with Hg intrusion results.d_(pore, 90% volume) is the pore diameter above which 90% of the totalpore volume exists.

*****d_(pore, 50% surface area) preferably determined by mercury (Hg)intrusion porosimetry, and more preferably as is set forth in ISO15901-1 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests, such as gas adsorption, fraybe employed to provide results that can be correlated with Hg intrusionresults. d_(pore, 50% surface area) is the pore diameter above which 50%of free surface area exists.

#Total Fe (wt %) preferably determined by dichromate titrimetry, andmore preferably as is set forth in ASTM E246-10 (the entire disclosureof which is incorporated herein by reference); recognizing that othertests, such as titrimetry after tin(II) chloride reduction, titrimetryafter titanium(III) chloride reduction, inductively coupled plasma (ICP)spectrometry, may be employed to provide results that can be correlatedwith dichromate titrimetry.

##Metallic Fe (wt %) preferably determined by iron(III) chloridetitrimetry, and more preferably as is set forth in ISO 16878 (the entiredisclosure of which is incorporated herein by reference); recognizingthat other tests, such as bromine-methanol titimetry, may be employed toprovide results that can be correlated with iron(III) chloridetitrimetry.

###Metallization (%) preferably determined by the ratio of metallic Feto total Fe, each as preferably determined by the methods previouslydescribed.

####Carbon (wt %) preferably determined by infrared absorption aftercombustion in an induction furnace, and more preferably as is set forthin ISO 9556 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests, such as various combustion andinert gas fusion techniques, such as are described in ASTM E1019-18 maybe employed to provide results that can be correlated with infraredabsorption after combustion in an induction furnace.

#####Fe²⁺ (wt %) preferably determined by titrimetry, and morepreferably as is set forth in ASTM D3872-05 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that othertests, such as Mossbauer spectroscopy, X-ray absorption spectroscopy,etc., may be employed to provide results that can be correlated withtitrimetry.

Fe³⁺ (wt %) preferably determined by the mass balance relation betweenand among Total Fe (wt %), Metallic Fe (wt %), Fe²⁺ (wt %) and Fe³⁺ (wt%). Specifically the equality Total Fe (wt %)=Metallic Fe (wt %)+Fe²⁺(wt %)+Fe³⁺ (wt %) must be true by conservation of mass, so Fe³⁺ (wt %)may be calculated as Fe³⁺ (wt %)=Total Fe (wt %)−Metallic Fe (wt %)−Fe²⁺(wt %).

$$ SiO₂ (wt %) preferably determined by gravimetric methods, and morepreferably as is set forth in ISO 2598-1 (the entire disclosure of whichis incorporated herein by reference); recognizing that other tests, suchas reduced molybdosilicate spectrophotometric methods, x-ray diffraction(XRD), may be employed to provide results that can be correlated withgravimetric methods. In certain methods, the SiO₂ wt % is not determineddirectly, but rather the Si concentration (inclusive of neutral andionic species) is measured, and the SiO₂ wt % is calculated assuming thestoichiometry of SiO₂; that is, a 1:2 molar ratio of Si:O is assumed.

$$$ Ferrite (wt %, XRD) preferably determined by x-ray diffraction(XRD).

$$$$ Wustite (FeO, wt %, XRD) preferably determined by x-ray diffraction(XRD).

-   -   $$$$$ Goethite (FeOOH, wt %, XRD) preferably determined by x-ray        diffraction (XRD).    -   + Cementite (Fe₃C, wt %, XRD) preferably determined by x-ray        diffraction (XRD).

The properties set forth in Table 2, may also be present in embodimentswith, in addition to, or instead of the properties in Tables 1 and/or1A. Greater and lesser values for these properties may also be presentin various embodiments.

In certain embodiments the DRI may be produced by the reduction of a DRGrade pellet, in which case the resulting DRI may have materialproperties as described in Table 3 below. The use of reduced DR gradeDRI may be advantageous due to the higher Fe content in the pellet whichincreases the energy density of the battery.

TABLE 3 Material Property Embodiment Range Specific surface area*0.1-0.7 m²/g as received or 0.19-25 m²/g after performing a pre-chargeformation step Actual density** 4.6-7.1 g/cc Apparent density*** 2.3-5.7g/cc Minimum d_(pore, 90% volume)**** 50 nm-50 μm Minimumd_(pore, 50% surface area)*****  1 nm-10 μm Total Fe (wt %)^(#)  80-94%Metallic Fe (wt %)^(##)  64-94% Metallization (%)^(###) 80-100% Carbon(wt %)^(####)   0-5% Fe²⁺ (wt %)^(#####)   0-8% Fe³⁺ (wt %)^($)   0-10%SiO₂ (wt %)^($$)   1-4% Ferrite (wt %, XRD)^($$$)  22-80% Wustite (FeO,wt %, XRD)^($$$$)   0-13% Goethite (FeOOH, wt %, XRD)^($$$$$)   0-23%Cementite (Fe₃C, wt %, XRD)⁺    «80% *Specific surface area preferablydetermined by the Brunauer-Emmett-Teller adsorption method (“BET”), andmore preferably as the BET is set forth in ISO 9277 (the entiredisclosure of which is incorporated herein by reference); recognizingthat other tests, such as methylene blue (MB) staining, ethylene glycolmonoethyl ether (EGME) adsorption, electrokinetic analysis ofcomplex-ion adsorption’ and a Protein Retention (PR) method may beemployed to provide results that can be correlated with BET results.**Actual density preferably determined by helium (He) pycnometry, andmore preferably as is set forth in ISO 12154 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that other testsmay be employed to provide results that can be correlated with Hepycnometry results. Actual density may also be referred to as “truedensity” or “skeletal density” in the art. ***Apparent densitypreferably determined by immersion in water, and more preferably as isset forth in ISO 15968 (the entire disclosure of which is incorporatedherein by reference); recognizing that other tests may be employed toprovide results that can be correlated with He pycnometry results.Porosity may be defined as the ratio of apparent density to actualdensity:${Porosity} = \frac{{apparent}\mspace{14mu}{density}}{{actual}\mspace{14mu}{density}}$****d_(pore, 90% volume) preferably determined by mercury (Hg) intrusionporosimetry, and more preferably as is set forth in ISO 15901-1 (theentire disclosure of which is incorporated herein by reference);recognizing that other tests, such as gas adsorption, may be employed toprovide results that can be correlated with Hg intrusion results.d_(pore, 90% volume) is the pore diameter above which 90% of the totalpore volume exists. ***** d_(pore, 50% surface area) preferablydetermined by mercury (Hg) intrusion porosimetry, and more preferably asis set forth in ISO 15901-1 (the entire disclosure of which isincorporated herein by reference); recognizing that other tests, such asgas adsorption, may be employed to provide results that can becorrelated with Hg intrusion results. d_(pore, 50% surface area) is thepore diameter above which 50% of free surface area exists. ^(#)Total Fe(wt %) preferably determined by dichromate titrimetry, and morepreferably as is set forth in ASTM E246-10 (the entire disclosure ofwhich is incorporated herein by reference); recognizing that othertests, such as titrimetry after tin(II) chloride reduction, titrimetryafter titanium(III) chloride reduction, inductively coupled plasma (ICP)spectrometry, may be employed to provide results that can be correlatedwith dichromate titrimetry. ^(##)Metallic Fe (wt %) preferablydetermined by iron(III) chloride titrimetry, and more preferably as isset forth in ISO 16878 (the entire disclosure of which is incorporatedherein by reference); recognizing that other tests, such asbromine-methanol titimetry, may be employed to provide results that canbe correlated with iron(III) chloride titrimetry. ^(###)Metallization(%) preferably determined by the ratio of metallic Fe to total Fe, eachas preferably determined by the methods previously described.^(####)Carbon (wt %) preferably determined by infrared absorption aftercombustion in an induction furnace, and more preferably as is set forthin ISO 9556 (the entire disclosure of which is incorporated herein byreference); recognizing that other tests, such as various combustion andinert gas fusion techniques, such as are described in ASTM E1019-18 maybe employed to provide results that can be correlated with infraredabsorption after combustion in an induction furnace. ^(#####)Fe²⁺ (wt %)preferably determined by titrimetry, and more preferably as is set forthin ASTM D3872-05 (the entire disclosure of which is incorporated hereinby reference); recognizing that other tests, such as Mossbauerspectroscopy, X-ray absorption spectroscopy, etc., may be employed toprovide results that can be correlated with titrimetry. ^($)Fe³⁺ (wt %)preferably determined by the mass balance relation between and amongTotal Fe (wt %), Metallic Fe (wt %), Fe²⁺ (wt %) and Fe³⁺ (wt %).Specifically the equality Total Fe (wt %) = Metallic Fe (wt %) + Fe²⁺(wt %) + Fe³⁺ (wt %) must be true by conservation of mass, so Fe³⁺ (wt%) may be calculated as Fe³⁺ (wt %) = Total Fe (wt %) − Metallic Fe (wt%) − Fe²⁺ (wt %). ^($$)SiO₂ (wt %) preferably determined by gravimetricmethods, and more preferably as is set forth in ISO 2598-1 (the entiredisclosure of which is incorporated herein by reference); recognizingthat other tests, such as reduced molybdosilicate spectrophotometricmethods, x-ray diffraction (XRD), may be employed to provide resultsthat can be correlated with gravimetric methods. In certain methods, theSiO₂ wt % is not determined directly, but rather the Si concentration(inclusive of neutral and ionic species) is measured, and the SiO₂ wt %is calculated assuming the stoichiometry of SiO₂; that is, a 1:2 molarratio of Si:O is assumed. ^($$$)Ferrite (wt %, XRD) preferablydetermined by x-ray diffraction (XRD). ^($$$$)Wustite (FeO, wt %, XRD)preferably determined by x-ray diffraction (XRD). ^($$$$$)Goethite(FeOOH, wt %, XRD) preferably determined by x-ray diffraction (XRD).⁺Cementite (Fe₃C, wt %, XRD) preferably determined by x-ray diffraction(XRD).

The properties set forth in Table 3, may also be present in embodimentswith, in addition to, or instead of the properties in Tables 1, 1A,and/or 2. Greater and lesser values for these properties may also bepresent in various embodiments.

In various embodiments, a bed of conductive pellets comprise (e.g.,function to provide, are a component of, constitute, etc.) an electrodein an energy storage system. In embodiments of this electrode thepellets comprise, an iron containing material, a reduced iron material,iron in a non-oxidized state, iron in a highly oxidized state, ironhaving a valence state between 0 and 3+ and combinations and variationsof these. In embodiments of this electrode the pellets comprise ironhaving one or more of the features set forth in Tables 1, 1A, 2, and 3.In embodiments the pellets have porosity, for example open porestructures, that can have pore sizes, for example, ranging from a fewnanometers to several microns. For example, embodiments may have poresizes from about 5 nm (nanometers) to about 100 μm (microns), about 50nm to about 10 μm, about 100 nm to about 1 μm, greater than 100 nm,greater than 500 nm, less than 1 μm, less than 10 μm, less than 100 μmand combinations and variations of these pore sizes as well as largerand smaller pores. In some embodiments, the pellets comprise pellets ofdirect reduced iron (DRI). Embodiments of these electrodes in the energystorage system, and in particular in long duration energy storagesystems, may have one or more of these foregoing features.

The packing of pellets creates macro-pores, e.g., openings, spaces,channels, or voids, in between individual pellets. The macro-poresfacilitate ion transport through electrodes that in some embodimentshave a smallest dimension that is still very thick compared to someother types of battery electrodes, being multi-centimeter in dimension.The micro-pores within the pellets allow the high surface area activematerial of the pellet to be in contact with electrolyte to enable highutilization of the active material. This electrode structure lendsitself specifically to improving the rate capability of extremely thickelectrodes for stationary long duration energy storage, where thickelectrodes may be required to achieve extremely high areal capacities.

The pellets for these embodiments, and in particular for use inembodiments of electrodes for long duration energy storage systems, canbe any volumetric shape, e.g., spheres, discs, pucks, beads, tablets,pills, rings, lenses, disks, panels, cones, frustoconical shapes, squareblocks, rectangular blocks, trusses, angles, channels, hollow sealedchambers, hollow spheres, blocks, sheets, films, particulates, beams,rods, angles, slabs, columns, fibers, staple fibers, tubes, cups, pipes,and combinations and various of these and other more complex shapes. Thepellets in an electrode can be the same or different shapes. The pelletsin an electrode that is one of several electrodes in a long durationenergy storage system, can be the same as, or different from, thepellets in the other electrodes in that storage system.

The size of the pellets, unless expressly used otherwise, refers to thelargest cross-sectional distance of the pellet, e.g., the diameter ofsphere. The pellets can be the same or different sizes. It beingrecognized that the shape, size and both of the pellets, as well as,typically to a lesser degree the shape and size of the container orhousing holding the pellets, determines the nature and size of themacro-pores in the electrode. The pellets can have sizes from about 0.1mm to about 10 cm, about 5 mm to about 100 mm, 10 mm to about 50 mm,about 20 mm, about 25 mm, about 30 mm, greater than 0.1 mm, greater than1 mm, greater than 5 mm, greater than 10 mm and greater than 25 mm, andcombinations and variations of these.

In embodiments, the pellets as configured in an electrode can provide anelectrode having a bulk density of from about 3 g/cm³ to about 6.5g/cm³, about 0.1 g/cm³ to about 5.5 g/cm³, about 2.3 g/cm³ to about 3.5g/cm³, 3.2 g/cm³ to about 4.9 g/cm³, greater than about 0.5 g/cm³,greater than about 1 g/cm³, greater than about 2 g/cm³, greater thanabout 3 g/cm³, and combinations and various of these as well as greaterand lesser values.

In certain embodiments a mixture of reduced DR grade and reduced BFgrade pellets may be used together. In certain other embodiments,reduced material (DRI) and raw ore materials (DR grade or BF grade) maybe used in combination.

In various embodiments, DRI may be produced by the use of an “artificialore” such as waste or by-product forms of iron oxide. As onenon-limiting example, mill scale is a mixed iron oxide formed on thesurface of hot rolled steel, which in various embodiments is collectedand ground to form an iron oxide powder which is then agglomerated toform a pellet and is subsequently reduced to form DRI. Other wastestreams may be similarly utilized to form DRI. As another non-limitingexample, pickle liquor is an acidic solution which can be rich indissolved Fe ions. In various embodiments, Fe-bearing pickle liquor maybe neutralized with a base (such as caustic potash or sodium hydroxide)to precipitate iron oxide powder which is then agglomerated to form apellet and is subsequently reduced to form DRI.

In various embodiments the precursor iron oxides are first reduced andthen subsequently formed into a pellet or other agglomerate. In certainnon-limiting embodiments iron oxide powder from a natural or artificialore is reduced to iron metal powder by heat treatment at 900° C. under areducing gas environment such as a linear hearth furnace with a hydrogenatmosphere, ranging from 1% to 100% H₂. In embodiments that use hydrogenas a reducing gas, the cementite (Fe₃C) content of the DRI can be as lowas 0 wt %.

In various embodiments, DRI pellets or agglomerates are formed in asingle process from iron oxide powders by use of a rotary calciner. Therotary motion of the furnace promotes agglomeration of the powder into apellet or agglomerate, while the high temperature reducing gasenvironment provides for concurrent reduction of the iron oxide. Invarious other embodiments a multi-stage rotary calciner may be used inwhich the agglomerating and reducing steps may be tuned and optimizedindependently.

In various embodiments, the DRI has a shape that is not spherical. Incertain embodiments the DRI may have a shape that is substantiallyrectilinear or brick-like. In certain embodiments the DRI may have ashape that is substantially cylindrical or rod-like, or disc-like. Incertain embodiments the DRI may have a shape that is substantiallyplanar or sheet-like. In certain embodiments the iron oxide powder isdry formed by die compaction into a cylindrical shape or any other shapethat is amenable to die pressing. In certain embodiments the iron oxidepowder is dry formed into a sheet-like form by roll pressing through acalendar roll. In certain embodiments the iron oxide powder is blendedwith a binder such as a clay or polymer and is dry processed into arod-like shape by extrusion. In certain embodiments the iron oxidepowder is blended with a binder such as a clay or polymer and is dryprocessed into a sheet-like form by roll pressing through a calendarroll. Binders may be comprised of a clay, such as bentonite, or apolymer, such as corn starch, polyacrylamide, or polyacrylate. Bindersmay include bentonite, sodium carbonate, calcium chloride, calciumhydroxide, sodium silicate, carboxymethylcellulose (CMC), Alcotac,Peridur, corn starch, Funa, wheat flour, sodium lignosulfate, molasses,or polyacrylate, etc. Binders may be comprised of a combination of oneor more clays and one or more polymers. In certain embodiments the ironoxide powder is dispersed into a liquid to form a slurry that is thenused to wet form into various shapes. In certain embodiments an ironoxide slurry is slip cast into a mold of near-arbitrary shape. Incertain embodiments an iron oxide slurry is coated onto a sheet bydoctor blading or other similar coating processes.

In various embodiments, a bed of conductive micro-porous pelletscomprise an electrode in an energy storage system. In some embodiments,said pellets comprise pellets of direct reduced iron (DRI). The packingof pellets creates macro-pores in between individual pellets. Themacro-pores facilitate ion transport through electrodes that in someembodiments have a smallest dimension that is still very thick ascompared to some other types of battery electrodes, being of multiplecentimeters in dimension. The macropores may form a pore space of lowtortuosity compared to the micro-pores within the pellets. Themicro-pores within the pellets allow the high surface area activematerial of the pellet to be in contact with electrolyte to enable highutilization of the active material. This electrode structure lendsitself specifically to improving the rate capability of extremely thickelectrodes for stationary long duration energy storage, where thickelectrodes may be required to achieve extremely high areal capacities.

In various embodiments, a fugitive pore former is incorporated duringthe production of DRI to increase the porosity of the resulting DRI. Inone embodiment, the porosity of the DRI pellet is modified byincorporating a sacrificial pore former such as ice (solid H₂O) in thepelletization process, which subsequently melts or sublimes away underthermal treatment. In certain other embodiments the fugitive pore formercomprises napthalene, which subsequently sublimes to leave porosity. Inother embodiments the fugitive pore former comprises NH₄CO₃ (ammoniumcarbonate) may be the fugitive pore former, and it may be introduced asa solid at various points in the production of DRI and will decomposeunder heat and leave entirely as gaseous or liquid species(NH₃+CO₂+H₂O). In various other embodiments, the fugitive additive mayserve an additional function in the cell (e.g. be an electrolytecomponent). In certain embodiments the fugitive additive may be analkaline salt such as KOH or NaOH or LiOH. In certain embodiments thefugitive additive may be a soluble electrolyte additive which is solidin form under ambient, dry conditions, such as lead sulfate, leadacetate, antimony sulfate, antimony acetate, sodium molybdenum oxide,potassium molybdenum oxide, thiourea, sodium stannate, ammoniumthiosulfate. In various other embodiments the fugitive additive may be abinder used in the agglomeration of iron ore powder to form a pellet orother shape, such as sodium alginate or carboxymethylcellulose binder.

In various embodiments, sacrificial pore formers, convertible poreformers, fugitive pore formers, removable pore formers, or techniquesmay be utilized. In these embodiments, the intermediate material withthe pore former still present may have Fe total wt % in the range of 20wt % to 90 wt %. The pore formers may be removed in part prior toutilization as an electrode, in whole prior to utilization as anelectrode, or during utilization as an electrode, and combinations andvariations of these. In an embodiment, an intermediate can have from 25wt % to 50 wt % Fe total, and upon removal of the pore former, providean electrode with 60 wt % to 90 wt % Fe total.

In certain embodiments, the reducing gas used to form DRI is hydrogen(H₂). In certain embodiments, the hydrogen used as reducing gas is abyproduct of an industrial, chemical, or manufacturing process. Incertain embodiments, the hydrogen is generated by electrolysis of waterfrom renewable power generation sources such as wind energy or solarenergy. In certain embodiments the electrolyzer is coupled to an energystorage system. In certain embodiments the electrolyzer is a ProtonExchange Membrane (PEM) electrolyzer. In certain embodiments theelectrolyzer is an alkaline electrolyzer. In certain embodiments, thehydrogen is a byproduct of a chloro-alkali process or plant. Inembodiments that use hydrogen as a reducing gas, the cementite (Fe₃C)content of the DRI can be as low as 0 wt %.

In certain embodiments, natural gas (methane, CH₄) is used as a reducingagent to produce DRI. In some embodiments, the natural gas used isobtained from naturally-occurring underground deposits or fromagriculture. In certain embodiments, the methane used as reducing gas isa byproduct of an industrial, chemical, or manufacturing process. Incertain embodiments, the methane is steam reformed (via reaction withwater, H₂O) to produce a mixture of carbon monoxide (CO) and hydrogen(H₂) through the reaction CH₄+H₂O→CO+3H₂. In certain embodiments, thisreforming reaction occurs through an ancillary reformer, separate fromthe reactor in which the iron reduction occurs. In certain embodiments,the reforming occurs in situ in the reduction reactor. In certainembodiments the reforming occurs both in an ancillary reformer and inthe reduction reactor. In certain embodiments, coal is used as areducing agent to produce DRI. In certain embodiments coke is used as areducing agent to produce DRI. In embodiments that use acarbon-containing reducing gas, the cementite (Fe₃C) content of the DRIcan be higher, up to 80 wt %.

In certain embodiments, a mixture of DRI produced using various reducinggases can be used to achieve a beneficial combination of composition andproperties. In one non-limiting embodiment a 50/50 mix by mass of DRIproduced from BF grade pellets reduced in natural gas and DRI producedfrom DR grade pellets reduced in hydrogen is used as the negativeelectrode of a battery. Other combinations of mass ratios, feedstocktype (DR, BF, other artificial ores, etc.) and reducing media (hydrogen,natural gas, coal, etc.) may be combined in other embodiments.

In various embodiments, DRI pellets may be crushed and the crushedpellets may comprise the bed (with or without the addition of a powder).

In various embodiments, additives beneficial to electrochemical cycling,for instance, hydrogen evolution reaction (HER) suppressants may beadded to the bed in solid form, for instance, as a powder, or as solidpellets.

In some embodiments, metal electrodes may have a low initial specificsurface area (e.g., less than about 5 m²/g and preferably less thanabout 1 m²/g). Such electrodes tend to have low self-discharge rates inlow-rate, long duration energy storage systems. One example of a lowspecific surface area metal electrode is a bed of DRI pellets. In manytypical, modern electrochemical cells, such as lithium ion batteries ornickel-metal-hydride batteries, a high specific surface area isdesirable to promote high rate capability (i.e., high power). In longduration systems, the rate capability requirement is significantlyreduced, so low specific surface area electrodes can meet targetrate-capability requirements while minimizing the rate ofself-discharge.

In some embodiments, DRI pellets are processed by mechanical, chemical,electrical, electrochemical, and/or thermal methods before the DRIpellets are used in an electrochemical cell. Such pre-treatments mayallow superior chemical and physical properties to be achieved, and, forexample, may increase the accessible capacity during the dischargereaction. The physical and chemical properties of as-purchased (alsosometimes referred to as “as received”) DRI may not be optimal for useas the negative electrode of an electrochemical cell. Improved chemicaland physical properties may include introduction of a higher content ofdesirable impurities, such as HER suppressants, achieving a lowercontent of undesirable impurities (such as HER catalysts), achieving ahigher specific surface area, achieving a higher total porosity,achieving a different pore size distribution from the starting DRI (suchas a multimodal pore size distribution to reduce mass transportresistance), achieving a desired distribution of pellet sizes (such as amultimodal size distribution to allow packing of pellets to a desireddensity), altering or selecting pellets of a desired aspect ratio (inorder to achieve a desired bed packing density). Mechanical processingmay include tumbling, milling, crushing, pulverizing, and powderizing.Chemical processing may include acid etching. Chemical processing mayinclude soaking a bed of pellets in an alkaline solution to createnecking between pellets, coarsen the micropores within the pellets, ordissolve impurity or secondary phases to increase the pore volumepercentage or alter the pore size distribution. Thermal processing mayinclude processing DRI at elevated temperature in inert, reducing,oxidizing, and/or carburizing atmosphere. In various embodiments,mechanical, chemical, electrical, electrochemical, and/or thermalmethods of pre-processing the materials forming an electrode, such asDRI pellets, etc., may fuse the material forming the electrode into abed, such as bed of fused together DRI pellets, etc.

In embodiments, as set forth herein, the iron material can be processed,chemically modified, mechanically modified, or otherwise configured, tohave one or more of its features changed. These methodologies aregenerally described herein as being performed on DRI material. It isunderstood that these methodologies can be used on other iron containingmaterials, such as, a reduced iron material, iron in a non-oxidizedstate, iron in a highly oxidized state, iron having a valence statebetween 0 and 3+ and combinations and variations of these. In thismanner there are provided iron containing pellets for utilization in anelectrode configuration for a long duration electrical storage cell thathave predetermined features, for example, the features as set forth inthis specification.

In certain embodiments, the DRI is subjected to mechanical operations togrind, abrade, or polish the surface, and/or remove fines. In oneembodiment, DRI pellets are rolled in a trommel screen to abrade thesurface and remove fine powder/dust from the surface. This operation mayhave the beneficial effect of reducing the reactivity of the pellet DRI,making it easier and safer to ship, without resorting to a briquettingor other compaction operation. In another embodiment, DRI blocks orsheets are passed under a rotary brush to remove fine powders from thesurface, having a similar beneficial effect.

In one embodiment, porosity is increased by pre-treating the DRI bysoaking in an acid bath (for example, concentrated HCl), which etchesthe iron and creates larger pores, increasing the total porosity. Theetching time can be optimized to increase the total capacity of a DRIpellet without losing too much active material to the acid etchingsolution.

In another embodiment, desirable impurities or additives areincorporated into DRI. When these impurities are solids, they may beincorporated by ball-milling (for example, with a planetary ball mill orsimilar equipment) the powder additive with DRI pellets, the pelletsserving as their own milling media. In this way the powder additive ismechanically introduced into the pores or surface of the DRI pellet. DRImay also be coated in beneficial additives, for example, by rolling ordipping in a slurry containing the additives. These desirable impuritiesmay include alkali sulfides. Alkali sulfide salts have been demonstratedto vastly improve active material utilization in Fe anodes. Just assoluble alkali sulfides may be added to the electrolyte, insolublealkali sulfides may be added to DRI, for example, by the above method.

In various embodiments, the specific surface area of DRI is increased bya factor of 3 or more, preferably a factor of 5 or more, as measured bya technique, such as the Brunauer-Emmett-Teller gas adsorption method.In some embodiments this surface area increase is accomplished by usingDRI as an electrode in an electrochemical cell, and electrochemicallyreducing it with an applied current.

In some embodiments, the surface area of cementite or iron carbidecontaining materials, such as DRI pellets containing cementite or ironcarbide, is increased by using the material as the anode of anelectrochemical cell and discharging it. In certain embodiments, thespecific current densities may be 0.1-25 mA/g. This high surface areairon oxide may also be used for various applications other than inelectrochemical cells.

In various embodiments, to increase electrical conductivity, pellets maybe mixed with a more electrically conductive, but potentially moreexpensive, powder, to produce a higher conductivity composite bed. Thispowder may increase the areal capacity of the cell by filling voids inbetween the pellets. This may decrease the ratio of electrolyte volumeto DRI pellets in a way that can be systematically varied and optimized.In one embodiment, this powder is used at the site of current collectionto increase the contact surface area, reducing interfacial resistivitybetween the current collector and the small contact area of thespherical pellets, as described in more detail in a previous section.This ensures the ability to vary and control the effective currentdensity at the pellet. Varying particle size in the composite bed mayproduce controllable cost and conductivity. In another example, the useof additional powder, wire, mesh, gauze, or wool conductive materialenables the use of low-conductivity pellets such as DR taconite pelletsor direct reduced pellets that are undermetallized (sometimes called“remet” in the trade) in the composite bed by increasing overallconductivity. In one embodiment, this conductive component may compriseDRI fines or other waste materials from the DRI process.

The ratio of electrolyte to iron material, for example DRI material in acell may be from about 0.5 mL_(electrolyte):1 g_(iron-material) to about5 mL_(electrolyte):1 g_(non-material), from about 0.6 mL_(electrolyte):1g_(iron-material) to about 3 mL_(electrolyte):1 g_(iron-material), about0.6 mL_(electrolyte):1 g_(iron-material), about 0.7 mL_(electrolyte):1g_(iron-material), about 0.8 mL_(electrolyte):1 g_(iron-material), about1 mL_(electrolyte):1 g_(iron-material), and combinations and variationsof these as well as larger and smaller ratios.

In one embodiment, porous sintered iron electrodes may be formed fromDRI, which may have its particle size reduced or be made into a powder,for instance, by crushing or grinding. DRI fines or other wastematerials may also be used to form a sintered iron electrode. Thesintered electrode may be formed with a binder under heat and/orpressure, then the binder may be burned out and the green-form issintered at high temperature. DRI pellets may also be directly fusedtogether by sintering, without a binder, optionally with pressureapplied, in a non-oxidizing atmosphere, in order to create electricaland physical connectivity between pellets.

In various embodiments, porous negative electrodes may be formed bycrushing, shredding, or grinding of hot briquetted iron (HBI). Invarious embodiments, HBI may be preferable for shipment andtransportation due to its lower surface area and reactivity, but theporosity of HBI may be too low for practical application in a thickelectrode, due to ionic transport limitations. To achieve the optimalcombination of transportation and performance, the DRI may betransported in a briquetted form to the cell assembly or manufacturingsite whereat it is crushed, ground, and/or shredded to increase theporosity of the resulting electrode.

A packed bed of DRI pellets may be a desirable configuration of aniron-based electrode as it provides for an electronically conductivepercolation path through the packed bed while leaving porosity availableto be occupied by an electrolyte that facilitates ion transport. Incertain embodiments, the ratio of electrolyte volume to DRI mass may bein the range of 0.5 mL/g to 5 mL/g, such as 0.6 mL/g or 1.0 mL/g. TheDRI pellets are generally in contact with surrounding pellets through asmall contact area compared to the surface area of the pellet, and insome instances the contact can be considered a “point contact.” Contactsof small cross-sectional area may be constrictions for the flow ofelectrical current that may result in a relatively low electricalconductivity for the pellet bed as a whole, which may in turn lead tohigh electrode overpotentials and low voltaic efficiency of the battery.

In various embodiments, the electrical conductivity of a DRI pellet bedmay be increased in a number of ways. In some embodiments, theelectrical conductivity of a DRI pellet bed may be increased by the useof an additional conductive material that may surround individualpellets, be embedded within individual pellets, surround the entirepellet bed, or penetrate through a pellet bed. The conductive materialmay be one or more of a metal, a metal oxide, a metal carbide, a metalnitride a semiconductor, carbon, a conductive polymer, or a compositecomprising at least one of such electronically conducting materials. Theelectronically conductive material may be in the form of a powder, wire,mesh, or sheet. In certain embodiments, the conductive material mayitself participate in an electrochemical reaction in the battery,including but not limited to providing storage capacity. In certainother embodiments the electronically conductive material is notsubstantially electrochemically active. In one embodiment, theconductive material is a powder, and the powder fills or partially fillsthe space between pellets or in between pellets and current collectorsto improve inter-pellet or pellet-to-current collector electricalconduction. For example, the conductive powder may consist of DRI“fines”, which is a powderized waste product of the direct reductionprocess that is similar in composition to DRI. The fines may serve toboth increase the electrical conductivity of the bed and to increase thestorage capacity of the anode in this case. In another embodiment, theconductive material is a powder, and the powder is applied to thesurfaces of the pellets to make a coating. Such a coating provides for alarger area for electrical contact between pellets.

In various embodiments, conductive coatings are applied tolow-conductivity pellets to enable their usage in an electrode. Incertain embodiments low-conductivity pellets such as taconite pellets ordirect reduced pellets that are undermetallized (sometimes called“remet” in the trade) may be coated. The coating may be conductive todecrease electrical resistance from the current collector to thetaconite pellet during the initial reduction step. The coating may ormay not be removed during or after the reduction step. In oneembodiment, the coating is a thin conformal metallic layer such asstainless steel that wraps circumferentially around each pellet. Inanother embodiment, the coating is a thin layer of lead that coats theoutside of each pellet using a directional deposition technique such assputtering, evaporation, or other physical vapor deposition techniques.In certain embodiments, the coating is applied by rolling DRI and thecoating material together in a rotating vessel. In certain embodimentsthe DRI in the rotating vessel is substantially spherical in shape.

In another embodiment, some or all of the individual pellets in thepellet bed are wrapped with an electrically conductive wire, foil orsheet. In some embodiments a tightening mechanism, such as a screen, isused to apply tension to the wire, foil or sheet. Optionally, suchcurrent collectors surrounding individual pellets can be attached towires that are gathered or connect to a larger current collector. Inanother example, a conductive mesh, gauze, or wool is interspersed inthe space between the DRI pellets to increase electrical connectivity.In various embodiments the conductive material is a mesh with an opening(clear size) that is selected to be smaller than the pellets such thatpellets do not pass through the mesh. The conductive material in thiscase may be stainless steel, nickel, or other metals and metal alloys.In another example, DRI pellets are directly connected to each other byconductive wire through or around the individual pellets. For example, awire may be threaded through holes in the DRI pellets, similar toforming a string of beads, leading to electrical contact not onlybetween pellets but to the interior of pellets. Optionally, a string ofpellets may be held in contact using an electrical terminal or “stopper”at which tension is optionally applied to the wire. The electricalterminals may optionally be electrically connected to a larger currentcollecting fixture such as a plate.

In another embodiment, the electrical conductivity of a bed of pelletsis improved by the application of a compressive load to the DRI pelletbed anode to increase inter-pellet force and/or pellet-to-pellet orpellet-to-current collector contact area, thus reducing contactresistance and enhancing electrochemical performance. Typical DRIpellets are approximately spherical in shape, have internal porosity,and can be elastically deformed to >5% linear strain before yielding.Applying a load that compresses the DRI bed can increase the effectivecontact area between pellets and at the interface between pellets andthe current collector. It is advantageous to use pellets with yieldstrains that permit deformation to achieve desired increases inconductivity without undergoing fracture. In one embodiment, pelletswith compressive strengths between 700 and 2500 psi are used in a pelletbed electrode to which a compressive load is applied. In addition, themechanical assembly that provides the compressive load on the pellet bedmay also serve as current collectors. The electrical resistance of sucha bed of pellets, measured in the dry state before any filling withliquid electrolyte, may be reduced by a factor of two to a factor of 100or more by applying a compressive load. In certain embodiments, theapplied load can be in the range of 0.1 psi to 1000 psi, such as 50 psior 100 psi. In certain embodiments, the applied load can be in the rangeof 0.1 psi to 10 psi, such as 1 psi or 5 psi. In one example, metalplates on opposing faces of a bed of pellets serve to provide bothcurrent collection and a compressive load on the pellet bed. Optionally,one or more of the plates may be replaced by a macro-porous currentcollector (e.g., metal mesh) to facilitate ionic transport throughoutthe electrode. The opposing current collectors are preferably joined sothey are at the same electrical potential, advantageously makingelectrochemical reaction rates more uniform throughout the electrode. Inanother example, a container containing the pellet bed serves both as acurrent collector and as a method of applying compressive load. Inanother embodiment, an array of conductive posts (or rods) that connectto a common, bottom-facing current collector is implemented. Therefore,many areas of current collection can be placed throughout the pelletbed. This approach can also reduce the effective transport lengthswithin the electrode from the total pellet bed thickness to theinter-post spacing. Additionally, these posts can be used to affix amechanical clamping mechanism, such as a plate or perforated plate atthe top of the pellet bed, to incorporate down-force onto the pelletbed, while serving as a current collection element.

In some embodiments, a compressive load may be provided in part or inwhole by a magnetic force. For example, force can be applied using apermanent magnet positioned on one or more sides of the bed, causing thepellets in the bed to be attracted to the magnet. For a DRI pellet bedthat is predominantly metallic iron, the pellet bed is expected to bepredominantly ferromagnetic, and the pellet bed would be attracted tothe magnet. The magnet can also be embedded in other fixturessurrounding the pellet bed. The magnets and fixtures serve to hold thebed of pellets in place, and provide a compressive stress that resultsin improved electrical contact between pellets and between pellets andcurrent collectors as described above.

In some embodiments, inter-pellet contact resistance in the pellet bedmay be reduced through the use of a pre-treatment applied to the pelletbed before battery assembly and/or operation. Several such pre-treatmentprocesses are described in the following paragraphs.

In some embodiments, whole DRI pellets are packed into a bed andsintered in an inert or reducing (i.e., non-oxidizing) atmosphere,optionally with the application of mechanical pressure during sintering,for example, using a material that is stable at the sinteringtemperature and atmosphere. The sintering temperature may range from600-1100° C. The non-oxidizing atmosphere may consist partially orwholly of inert gases such as nitrogen or argon. The non-oxidizingatmosphere may also include mixtures of gases that tend to reduce iron,such as CO and CO₂, and H₂ and H₂O. The exact composition of the mixturemay be optimized according to an Ellingham diagram to ensure thatoxidation of the iron is thermodynamically unfavorable. In oneembodiment, forming gas (5% H₂, 95% N₂) is used at a sinteringtemperature of about 600° C. to about 1100° C., such as 600° C. to about850° C., 850° C., about 850° C. to about 1100° C., etc., to provide anon-oxidizing condition. The combination of high temperature and anon-oxidizing atmosphere may promote atom diffusion and particlecoarsening at pellet contacts, causing the pellets to bond to eachother. The result is a bed of DRI pellets that are fused together withlow inter-pellet contact resistance. The pellets may also be fused tothe current collector through the same process.

In another embodiment, the pellets are joined using a thermal treatmentin which a flux or sintering aid is used to substantially reduce theheat treatment temperature required to form sinter necks between thepellets. Examples of fluxes or sintering aids include one or more metalsof lower melting point than iron, such as zinc, tin, copper, aluminum,bismuth, and lead, or metals which form alloys with iron that have lowermelting temperatures than iron, such as those which exhibit alower-melting eutectic liquid. Other examples of sintering aids includeone or more glass-forming compositions including but not limited tosilicates, borates and phosphates.

In another embodiment, the pellets can be fused together electrically bya process such as welding. In some such embodiments, welding isaccomplished by passing electrical current through the bed of pellets.In some such embodiments, such current is delivered by discharging acapacitor.

In various embodiments the anode electrode is an ordered array ofpellets. In certain embodiments the pellets are arranged into cylinders.In certain embodiments the pellets are arranged into plates. In certainembodiments the pellets are arranged into discs. In certain embodimentsthe pellets are arranged into rectangular prisms. In certain embodimentsthe pellets are arranged into hexagonal prisms. In certain embodimentsthe pellets are arranged into arbitrary volumes.

In various embodiments, an electrolyte management system may beprovided, in which different electrolyte additives or formulations areadded to the battery when switching between states of operation. Theoptimal electrolyte formulation for operation during the charge,discharge, and idle states of a battery may be very different. Theelectrolyte management system of various embodiments may improvecapacity utilization of the iron electrode, self-discharge of the cell,and suppress the hydrogen evolution reaction (HER). One or more suchbenefits may be realized simultaneously. In one embodiment of such anelectrolyte management system, an arbitrary number of distinctelectrolyte formulation reservoirs are provided, each connected to theelectrochemical cell with separate flow controllers. During differentstages of operation, different relative amounts of each electrolyteformulation are flowed into the cell based on the optimal concentrationsof constituent species for the instantaneous mode of operation (charge,discharge, idle). The electrolyte management system may be configured toadjust the electrolyte composition based on the instantaneous state ofcharge of the battery.

Various embodiments may provide a method and apparatus for maintainingthe liquid electrolyte level in a battery. A vessel containing waterwhen exposed to air will experience evaporation until the partialpressure of water vapor in the air is equal to the vapor pressure ofwater at the system's temperature. Specifically, an electrochemicalsystem where aqueous electrolyte is exposed to the environment willexperience this same evaporation. Dehydration of the electrolyte canlead to issues stemming from reduced electrolyte volume, and changes inelectrolyte concentration can alter electrochemical performance. Tomitigate this issue, in various embodiments the electrolyte level may bemaintained via constant or intermittent flow of electrolyte into thecell volume. Specifically, electrolyte liquid level can be maintained byintroduction of electrolyte into the vessel until it pours over anoverflow point. Since the liquid level cannot rise above this spillpoint, the level can be maintained in a relatively controlled manner.Specifically, several volumes can be arranged in a cascade such thatoverflow from one chamber can flow into the next, establishing “liquidcommunication” between cells. Linking these cells in series allows onesource to supply liquid electrolyte to several cells simultaneously.Overflow from the final vessel can be re-circulated to the first. In asystem that utilizes shared electrolyte, flowing in a cascading fashionbetween cells, attributes of the electrolyte can be monitored andtreated at a central location for many cells. Electrolyte mediation suchas performing compositional adjustments or adding components, in orderto mitigate issues related to electrolyte carbonation, electrolytedehydration, and the like, is beneficially conducted at such acollection source for the circulating electrolyte.

Various embodiments may provide compositions and methods for addingbeneficial additives to the electrolyte of an aqueous electrochemicalcell are provided. During charging of an aqueous secondary battery,electrolytic production of hydrogen can cause coulombic inefficiency,gas buildup in the cell housing, safety concerns, and consumption ofelectrolyte. Furthermore, metal electrode self-discharge can occur byspontaneous reaction of the metal with the electrolyte to form metalhydroxide, in which reaction hydrogen is produced as a product. Certainsolid-phase hydrogen evolution inhibitors (e.g., Bi, Sb, As) can reducethese deleterious effects, but incorporating a solid-phase inhibitorinto the porous metal electrode of a battery can be costly and presentmanufacturing challenges. Accordingly, various embodiments, a solublesalt of a desired hydrogen evolution inhibitor, which dissolves toprovide in solution ions of the desired additive (e.g., Bi³⁺, Sb³⁺,As³⁺), is added to a liquid electrolyte. The additive is selected suchthat the redox potential of the inhibitor's ion-to-metal platingreaction (e.g., Bi³⁺→Bi⁰) occurs at a higher half-cell potential (asmeasured vs. RHE (but at a lower cell potential)) than the potential ofthe charging reaction of the anode active material. Thus, duringcharging of the battery (reduction of the metal electrode), the ionicform of the HER inhibitor is electrodeposited onto the surfaces of themetal electrode, providing an inexpensive and simple strategy forintroducing an HER inhibitor to the battery electrolyte chemistry. Theelectrodeposited inhibitor suppresses the hydrogen evolution reaction atthe surface of the electrode, which may be an electrode with openporosity. During the discharge mode, the deposit may dissolve back intothe electrolyte. The salt additive is preferably selected so that itdoes not degrade the operation of the cathode during charge or dischargeoperations.

In another embodiment, the electrochemical cell includes an electrode atwhich the hydrogen oxidation reaction (HOR) is performed to recapturethe hydrogen produced in the HER side reaction, mitigating the evolutionof potentially dangerous hydrogen gas. Hydrogen gas bubbles generatedduring HER may be captured and exposed to the HOR electrode, which maybe a working electrode of the battery cell or an additional electrodeadded to the system. In one embodiment, the hydrogen gas is captured byarranging the electrodes of the cell such that buoyancy forces carry thehydrogen gas bubbles to the HOR electrode. For example, the system maybe tilted, or include a funnel designed to promote this flow.

In various embodiments, a liquid electrolyte is flowed through acollection or bed of DRI pellets. For a thick (up to multi-centimeter)battery electrode comprised of active material pellets, it can bechallenging to achieve sufficient transport of reactants, reactantproducts, and additives through the thick bed on a time scalecommensurate with the operating (charge and discharge) time scale of thebattery. Inadequate transport rates in the electrolyte can have severaldetrimental impacts including but not limited to increasingoverpotential losses in the pellet-based electrode and decreasingutilization of the active materials. In a metal-electrode battery withan alkaline electrolyte, bubble formation and pH gradient formationduring both charge and discharge conditions may result in undesiredperformance decay or corrosion of one or both of the electrodes. Invarious embodiments, liquid electrolyte is flowed through the bed of DRIpellets in order to reduce the detrimental effects of limited transport.Flow of the electrolyte produces convective transport of electrolyteindividual pellets. Amongst other benefits, electrochemical reactionrates and uniformity of reaction are improved by decreasing electrolyteconcentration boundary layers that may arise through the thickness ofthe entire pellet bed or within macro-pores in the pellet bed. Theelectrolyte flow will generally decrease overpotential losses byhomogenizing the electrolyte composition throughout the macro- andmicro-structure of the electrode. In some embodiments, electrolyte flowis accomplished using active methods, such as mechanical pumping. Theflow rate of the electrolyte may be low, as low as 1 mL/min/cm² or less.In other embodiments, electrolyte flow is accomplished by passive means,such as buoyancy-driven flow due to thermal or compositional gradients.In a specific example, a component of the battery at which resistivedissipation of heat occurs is located at or near the bottom of theelectrode bed, causing electrolyte to be heated and to rise through thebed of pellets. In another specific example, an electrode at which anelectrochemical reaction changes the density of the electrolyte, forexample via an exothermic or endothermic reaction or a change in thecomposition of the electrolyte in contact with the electrode, is locatedwithin the battery so as to produce buoyancy-driven flow. In thisexample, an electrode reaction that produces a lower density electrolytemay be located at or near the bottom of a bed of DRI pellets, and areaction that increases the density of the electrolyte may be located atthe top of the bed of pellets.

In some embodiments, an additive that suppresses a side-reaction, suchas a corrosion inhibitor that suppresses the HER reaction or suppressesself-discharge, is combined with an additive that improves capacityutilization. Additives to the electrolyte of a battery comprising ametal electrode, including iron electrodes, may beneficially performseveral functions including increasing the capacity utilization of theiron, suppressing undesirable side reactions, or both. Differentadditives have different advantages, and these advantages can becombined by combining additives in the proper concentration. An exampleof a utilization enhancing additive is sulfur or a sulfide. In someembodiments, more than one corrosion inhibitor may be used with one ormore sulfides. For example, sulfur aids in de-passivation of ironelectrodes, but may be consumed during electrochemical cycling of thebattery. Sulfur consumption may therefore contribute to a fade incapacity over many cycles. In one embodiment, a delivery system is usedto replenish sulfur in order to maintain battery performance One exampleof such a system is a pump that delivers sulfur-bearing liquid to thebattery cell. Another example is a dry hopper that delivers polysulfidesalts to a closed or open battery cell.

In one embodiment, iron sulfide (FeS) may added to a metal-air batterythat uses an alkaline electrolyte as a sparingly soluble additive,thereby improving the electrochemical stability of the OER electrode andincreasing the electrode lifetime. This embodiment aids in mitigatingcatalyst performance decay at an oxygen evolution reaction (OER)electrode under alkaline conditions, which may limit the operationallifetime of the electrode.

In certain embodiments sulfur may be added to DRI by an additionalprocess operation. In certain embodiments DRI may be dipped in a moltensulfur bath, taking advantage of the low melting temperature of sulfur.In certain other embodiments, hydrogen sulfide gas may be flowed overhot or cold DRI to deposit a layer of sulfur and/or iron sulfide on thesurface of the DRI. In certain other embodiments sulfur may be sublimedand vapor deposited on the surface of the DRI; the DRI may be hot orcold. In certain embodiments sulfur is melt diffused into the pores ofDRI by melting sulfur and then wicking it into the pores of DRI.

In some embodiments, sulfur may be added to the DRI by a wet depositionprocess involving a process solvent. In certain embodiments, colloidalmixtures may be used to deposit sulfur or sulfide (e.g., FeS) specieson/within the DRI. For example, a dispersion of sulfur in water may beprepared via sonication to which DRI is subsequently added. The watermay be allowed to evaporate, depositing the sulfur or sulfide species onthe surface and within the DRI pellets. In certain other embodiments,sulfur may be dissolved in an organic solvent (e.g., ethanol oracetone). Addition of DRI to the solution, and subsequent evaporation ofthe solvent, allows for a coating of sulfur.

In some embodiments, additives comprising a molybdate ion are used in analkaline battery comprising an iron anode. Without being bound by anyparticular scientific interpretation, such additives may aid insuppressing the hydrogen evolution reaction (HER) at the iron electrodeand improving the cycling efficiency of the battery. The concentrationof the additive is selected to be able to suppress HER while stillenabling the desired iron charge/discharge process. As an example, amolybdate ion may be added via a molybdate compound such as KMoO₄. Inone specific example, the electrolyte contains an additive concentrationof 10 mM (mM means millimolar, 10⁻³ mol/L concentration) molybdateanion. In other embodiments, the electrolyte contains additiveconcentrations ranging from 1-100 mM of the molybdate anion.

In some embodiments, a surfactant is used to control wetting andbubbling during operation of a metal air battery. During charging, atleast two gas evolution reactions may occur that result in bubbleformation. One is hydrogen evolution at the metal anode, which is aparasitic reaction that may contribute to poor coulombic efficiencyduring cycling of the battery. Another is the oxygen evolution reaction,which is necessary for the functioning of the metal-air battery. Asurfactant additive can mitigate undesirable effects associated withboth reactions. In the case of HER, a hydrophobic surfactant additivemay suppress the hydrogen evolution reaction at the metal anode byphysically blocking water (a HER reactant) from the metal anode duringcharging. In the case of ORR, a surfactant additive may reduceelectrolyte surface tension and viscosity at the oxygen evolutionelectrode to generate smaller, uniformly sized, controllable bubblesduring charging. In one non-limiting example, 1-Octanethiol is added tothe alkaline electrolyte at a concentration of 10 mM to mitigate both ofthese challenges.

In some embodiments, a carbonate salt is added to the electrolyte of ametal-air battery utilizing an alkaline electrolyte in order to lowerthe rate of uptake of carbon dioxide from the air. In air, potassium orsodium hydroxide based electrolytes will lose potassium or sodiumcations from solution through a reaction with the carbon dioxide (CO₂)present in air, forming potassium or sodium carbonate. This especiallyposes a problem for batteries with an air electrode, since ambient airsupplies the lowest-cost form of the desired reactant, oxygen, to theoxygen reduction reaction (ORR) electrode. Electrolyte carbonation canlead to several detrimental effects on battery performance relating toundesired side reactions and decreased electrolyte conductivity, all ofwhich contribute to lower operating efficiency of the battery. The rateof carbonate formation, however, slows dramatically with increasedcarbonate concentration in the electrolyte. In one embodiment, acarbonate salt is intentionally added to the electrolyte beforeoperation to decrease the rate of the carbonation reaction with airwhile the battery is in operation. The intentional carbonate additionmitigates the deleterious effects of carbonation and maintainsacceptable carbonate levels in the electrolyte over a long operationallifetime.

In an embodiment, the health of the electrolyte in a metal air batteryis periodically or continuously monitored. Electrolyte age and qualityare found to dramatically impact the electrochemical performance of aniron-air battery. In some instances, the degradation of performance isassociated with the negative electrode, for instance, an iron electrode.Generally, as the electrolyte ages, the discharge capacity of thenegative electrode decreases. This may be due to changing concentrationsof electrolyte constituents over time due to spontaneous reactions thatform undesired products, especially those due to exposure to air. Insome embodiments, electrolyte health is monitored while the battery isin operation in order to determine the appropriate time to replenish,replace, or treat the electrolyte. The feedback mechanism may be manualor automated. In an automated system, the electrolyte qualitymeasurement may be one input to a proportional-integral-derivative (PID)loop that adjusts electrolyte constituent concentrations on a continuousbasis. The electrolyte quality measurement is done ex-situ on a smallaliquot of the electrolyte, or is done operando on the activeelectrolyte while the cell is in operation. One non-limiting method forassessing electrolyte health is to measure the electrical conductivityof the electrolyte. One mechanism of degradation is carbonation of theelectrolyte over time, due to CO₂ dissolution in the electrolyte fromair. In a specific example, experiments are performed to show thatelectrolyte conductivity varies in linear proportion to the carbonateconcentration in the electrolyte. A conductivity probe is used toevaluate the concentration of carbonate in the electrolyte. Theconductivity probe is used to monitor the state of health of theelectrolyte.

In some embodiments, corrosion inhibitors used in the field of ferrousmetallurgy to inhibit aqueous corrosion are used as components in abattery with an iron negative electrode to improve performance. In someembodiments, directed reduced iron (DRI) is used as the negativeelectrode, and favorable performance characteristics may be achieved byusing one or more corrosion inhibitors in a suitable range ofconcentrations. In these embodiments, the principles of corrosionscience are used to prevent undesirable side reactions (e.g. hydrogenevolution) in the charge condition, mitigate the rate of spontaneousself-discharge during an electrochemical hold, and maximize theutilization of iron active material upon discharge. Generally, there aretwo classes of corrosion inhibitors: interface inhibitors which reactwith the metal surface at the metal-environment interface to preventcorrosion, and environmental scavengers that remove corrosive elementsfrom the environment surrounding the metal surface to inhibit corrosion.Under the broad umbrella of corrosion inhibitors, appropriateconcentrations of inhibitors may be added to the electrochemical cell toachieve favorable performance characteristics with respect to theefficiency and capacity of an electrochemical cell. For the ironelectrode of a metal air battery, one applicable general class ofinhibitors are liquid and interphase interface inhibitors. This classencompasses three major types of interface inhibitors: anodic, cathodic,and mixed inhibitors. Anodic inhibitors create a passivation layer thatinhibits an anodic metal dissolution reaction. Cathodic inhibitors maydecrease the rate of a reduction reaction (HER in the case of an ironelectrode), or precipitate at cathodic active sites to block the samereduction reaction. Mixed inhibitors may inhibit corrosion via one orboth pathways, and include but are not limited to molecules that adsorbon the metal surface physically or chemically to form a film that mayblock active sites for a reduction reaction. The inhibitors can be addedto a base electrolyte at any concentration.

In various embodiments, an inhibitor that forms a passivation layer onthe metal surface is paired with an additive that de-passivates the ironsurface. In the correct concentrations, an optimal balance of corrosioninhibition and active material utilization may be achieved. In onespecific embodiment, when using direct reduced iron as the negativeelectrode, 10 mM molybdate anion is used as the passivator, while 10 mMsulfide anion is used as the de-passivator in an alkaline electrolytecomprised of 5.5M potassium or sodium hydroxide. Specific examples ofelectrolyte compositions include: 5.5 M KOH+0.5 M LiOH+10 mM Na₂S+10 mM1-octanethiol; 5.95 M NaOH+50 mM LiOH+50 mM Na₂S+10 mM 1-octanethiol;5.95 M NaOH+50 mM LiOH+50 mM Na₂S+10 mM 1-octanethiol+10 mM K₂MoO₄; and5.95 M NaOH+50 mM LiOH+50 mM Na₂S+10 mM K₂MoO₄. However, the presentdisclosure is not limited to any particular concentration of the aboveadditives in the electrolyte. For example, one or more of the aboveadditives may be included in the electrolyte at concentrations rangingfrom about 2 mM to about 200 mM, such as from about 5 mM to about 50 mM,or about 5 mM to about 25 mM.

In certain embodiments, other electrolyte additives are incorporated inthe electrolyte. Electrolyte additives may be selected from thenon-limiting set of sodium thiosulfate, sodium thiocyanate, polyethyleneglycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolvingZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodiumpermanganate, lead (IV) oxide, lead (II) oxide, magnesium oxide, sodiumchlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoricacid, sodium phosphate, ammonium sulfate, ammonium thiosulfate,lithopone, magnesium sulfate, iron(III) acetylacetonate, hydroquinonemonomethyl ether, sodium metavanadate, sodium chromate, glutaric acid,dimethyl phthalate, methyl methacrylate, methyl pentynol, adipic acid,allyl urea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilyl propyl diethylene,aminopropyl trimethoxysilane, dimethyl acetylenedicarboxylate (DMAD),1,3-diethylthiourea, N,N′-diethylthiourea, aminomethyl propanol, methylbutynol, amino modified organosilane, succinic acid, isopropanolamine,phenoxyethanol, dipropylene glycol, benzoic acid,N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutanetricarboxylic, mipa borate, 3-methacryloxypropyltrimethoxysilane,2-ethylhexoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate,diisopropanolamine, propylene glycol n-propyl ether, sodiumbenzotriazolate, pentasodium aminotrimethylene phosphonate, sodiumcocoyl sarcosinate, laurylpyridinium chloride, steartrimonium chloride,stearalkonium chloride, calcium montanate, quaternium-18 chloride,sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate,calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodiumbisulfide, pyrite, sodium nitrite, complex alkyl phosphate ester (e.g.RHODAFAC® RA 600 Emulsifier), 4-mercaptobenzoic acid,ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA),1,3-propylenediaminetetraacetate (PDTA), nitrilotriacetate (NTA),ethylenediaminedisuccinate (EDDS), diethylenetriaminepentaacetate(DTPA), and other aminopolycarboxylates (APCs),diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanethiol,bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III)oxide, antimony(V) oxide, bismuth selenide, antimony selenide, seleniumsulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol,1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol,trans-cinnamaldehyde, Iron(III) sulfide, calcium nitrate,hydroxylamines, benzotriazole, furfurylamine, quinoline, tin(II)chloride, ascorbic acid, tetraethylammonium Hydroxide, calciumcarbonate, magnesium carbonate, antimony dialkylphosphorodithioate,potassium stannate, sodium stannate, tannic acid, gelatin, saponin,agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithiummolybdenum oxide, potassium molybdenum oxide, hydrotreated lightpetroleum oil, heavy naphthenic petroleum oil (e.g. sold as Rustlick®631), antimony sulfate, antimony acetate, bismuth acetate,hydrogen-treated heavy naphtha (e.g. sold as WD-40®),tetramethylammonium hydroxide, NaSb tartrate, urea, D-glucose, C₆Na₂O₆,antimony potassium tartrate, hydrazinsulphate, silica gel,triethylamine, potassium antimonate trihydrate, sodium hydroxide,1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea,1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N′-diphenylthiourea,sodium antimonyl L-tartrate, rhodizonic acid disodium salt, sodiumselenide, and combinations thereof.

In certain embodiments the electrolyte is gelled. In certainembodiments, silica (SiO₂) or other network forming oxides such as boronoxide (B₂O₃) or alumina (Al₂O₃) are dissolved in an alkaline liquid toform a gel. In certain embodiments, a network-forming organic moleculeis dispersed in a liquid electrolyte to form a gel electrolyte. Incertain embodiments, the organic molecule comprises a polymer. Incertain embodiments a liquid electrolyte is added to a solid polymersuch as polyethylene oxide (PEO), polyvinyl alcohol (PVA),polyacrylamide (PAM), or polyacrylic acid (PAA) to form a gelelectrolyte. Bio-derived polymers, such as cassava or gelatin, may alsobe used as the polymer additive. In certain embodiments the gelelectrolyte is formed in situ by dissolution of silica (or other oxides)from DRI. In certain other embodiments, additional gel-former isintentionally added to a liquid electrolyte for purposes of creating agel. In certain embodiments a gel electrolyte is formed in situ due tothe evaporation of solvent (e.g. water) from the electrolyte,concentrating the dissolved salts and converting the electrolyte from aliquid to a gel or supersaturated solution.

In certain embodiments the electrolyte is a semi-solid or slurryelectrolyte. In certain embodiments the liquid is supersaturated withsalt and the electrolyte is a two-phase mixture of solid salt andsaturated solution. In certain embodiments, the electrolyte may be asaturated solution of NaOH in water with additional dispersed solidphase NaOH, which together forms a slurry electrolyte. Such anelectrolyte may have mechanical properties similar to those of a gel.

In certain embodiments, electrolyte additives are delivered to theelectrode as mixtures of solids. Electrolyte additives may have a rangeof solubilities, and some may have the most beneficial effect when theyare intimately mixed with the solid electrode. In one embodiment, thesolid pellets are primarily composed of additives, and these additivepellets are added to or mixed with a metal electrode, which in oneembodiment comprises multiple DRI pellets. In another embodiment, theelectrolyte additives are mixed with a metal, which may be the metalcomprising the redox-active electrode, and this mixture, which may bepelletized, is mixed with a metal electrode, which in one embodimentcomprises multiple DRI pellets. Non-limiting examples of additivesinclude sodium sulfide (Na₂S), potassium sulfide (K₂S), lithium sulfide(Li₂S), iron sulfides (FeS_(x), where x=1-2), bismuth sulfide (Bi₂S₃),lead sulfide (PbS), zinc sulfide (ZnS), antimony sulfide (Sb₂S₃),selenium sulfide (SeS₂), tin sulfides (SnS, SnS₂, Sn₂S₃), nickel sulfide(NiS), molybdenum sulfide (MoS₂), and mercury sulfide (HgS), FeS,bismuth oxide (Bi₂O₃), combinations thereof, or the like. In someembodiments, pellets are prepared with varying proportions ofredox-active metal to additive, and pellets differing in composition aremixed to create a blended electrode.

In some embodiments, an electrochemical formation cycling protocol isused to change the properties of starting DRI pellets and improvesubsequent operational electrochemical performance of the DRI as ananode. As-made DRI pellets may not be in a form optimized forelectrochemical cycling in a battery. For example, a native oxide mayexist on the free surface of the DRI that blocks electrochemical accessto active material; the specific surface area may be too low to reachdesired specific capacity; and/or the pore structure may limit ionictransport and limit specific capacity. In one specific embodiment,initial cycling, referred to as “formation,” consists of one or morerepetitions of one or more of the following steps. One step may be abrief charging step (“pre-charge”), during which any native oxide layerthat detrimentally passivates the as-received DRI may be chemicallyreduced, or the specific surface area of the DRI pellet may beincreased, in some cases by more than a factor of 10. These changes mayincrease the accessible capacity of the DRI in subsequent discharges.Another step may be a discharge step that oxidizes the metallic ironuntil one or more of the reactions from Fe to Fe²⁺, or Fe²⁺ to Fe³⁺, arefully or partially completed. The charge and discharge capacities may bedifferent between repetitions of the formation cycle. In someembodiments, formation may comprise repeated pre-charge and dischargecycles of systematically increasing capacity. In one specificembodiment, the formation cycling consists of the following: Pre-chargeto a capacity of 250 mAh/g, then cycle n times the following loop:discharge to 25+n*25 mAh/g, then charge to (25+n*25)*1.1 mAh/g, where nis the cycle number. The pre-charge step increases the specific surfacearea of the DRI from about 0.5 m²/g up to 12 m²/g or greater, which mayenhance accessible capacity for subsequent discharges. The rest of theformation cycling is conducted over n cycles, in growing capacityincrements of 25 mAh/g (assuming a 90% coulombic efficiency), graduallyapproaching charge and discharge capacities corresponding to deepcycling.

In some embodiments, the electrical potential at which the negativeelectrode is charged is controlled using particular operationalstrategies. During charging of an iron-air battery, iron reduction andthe parasitic hydrogen evolution reaction are expected to occurconcurrently over a large potential range, but the relative rates ofeach reaction are potential-dependent. Over some potential regimes, thehydrogen evolution reaction will be thermodynamically and/or kineticallyfavored, whereas in others, the iron reduction reaction will be favored.Strategies that involve tuning of the operating potential of thenegative electrode during charge include, but are not limited to, thefollowing strategies. For example in one strategy the negative electrodeis charged at a higher current rate than the rate at which it isdischarged. This may be affected during constant current, constantpower, or other more complex cycling conditions. By charging at agreater rate than that during discharging, the electrode may be drivento a potential that thermodynamically and/or kinetically favors thereduction of iron rather than parasitic reactions like hydrogenevolution. The result is a higher coulombic efficiency and higherelectrode utilization over multiple cycles. As another example, inanother strategy the negative electrode is charged at constant potentialinstead of constant current or power. The charging potential is selectedto optimize electrochemical performance. For example, the potential oncharge may be optimized to maximize coulombic efficiency and higherelectrode utilization. As another example, in another strategy theeffective resistance of other cell components (i.e., not the solid Feelectrode or negative current collector) in increased. By doing so, alarger overall cell polarization is achieved, which causes the negativeelectrode to have larger polarization. If the extra negative electrodepolarization is sufficiently large, the absolute potential of the Feelectrode may become sufficiently low to favor iron reduction over thehydrogen evolution reaction. This effect can be achieved by increasingthe effective resistance of the electrolyte, cathode, or cathode currentcollector.

In some embodiments, self-discharge of the negative electrode is limitedby using a passivating chemical layer on the metal anode, optionallyused with one or more electrical pulses during charging. Metal anodes(e.g., Fe, Al, Zn) in alkaline batteries typically self-dischargethrough a corrosion reaction, that forms hydrogen gas and metalhydroxide as a product of the self-discharge corrosion reaction.Typically, passivating electrolyte additives are considered undesirablefor slowing self-discharge because the passivation layer also makes themetal anode non-reactive in desired discharge reactions. According tothe present embodiment, an electrolyte additive (e.g., Na₂MoO₄) is usedthat forms a thin, passivating film. Self-discharge of the anode istherefore limited to only a small layer on the surface of the anode.However, to recover reactivity of the metal anode, a short andaggressive charging pulse is used to reduce the surface film. Once thesurface film is reduced, the discharge reaction can proceed.

In this embodiment, an ex-situ measurement of the composition of themetal electrode is used to determine its state of charge and state ofhealth. In an electrochemical cell that comprises an iron electrode, thestate of charge and state of health of the electrode are correlated withthe fraction of metallic iron. Therefore, measurement of the fraction ofmetallic iron can be used to identify the battery's state of charge orstate of health. In one specific embodiment, magnetic susceptibilitymeasurements are performed on one or more portions of an iron electrodeto determine state of charge or state of health. In order to conductsuch measurements, the sample may be shaped it into a disc or cylinder,with a thickness in the range of several millimeters and a diameter of0.25 cm to 4 cm. The measured magnetic susceptibility is analyzed toextract the relative amounts of metallic iron, ferrous iron, and ferriciron.

In various embodiments, DRI is used as a redox-active electrode materialin a battery of primary or secondary type. In one embodiment DRI is usedas an anode active material in a primary battery. In one embodiment DRIis used as an anode active material in a primary refuelable (ormechanically rechargeable) primary battery in which the anode ismechanically replaceable by fresh DRI. In one embodiment, DRI is used asan anode active material in a secondary battery. In another embodiment,DRI is used as an electrode material with alkaline electrolyte (pH>9).In one particular embodiment, the alkaline secondary battery may employa nickel cathode. In this embodiment, DRI serves as the startingmaterial for the anode of a Ni—Fe alkaline secondary battery, and may beused in its as-received state or may be processed before use accordingto other embodiments described herein. Other electrochemical couples(combinations of a cathode and an anode) for alkaline batteriesemploying a DRI anode include iron/nickel (Fe/Ni cell) or iron/silver(Fe/Ag cell). In various embodiments, DRI may serve as an anode activematerial in primary or secondary batteries where the pH of the electrodespans the acidic (pH<5.5) or neutral (5.5<pH<9) regimes. As an example,DRI may be used as the anode active material in a battery employing anelectrolyte containing hydrochloric acid (HCl) in the concentrationrange of 1-5 M. At the anode, the DRI may engage in the followinghalf-cell reaction upon discharge: Fe+2Cl⁻→FeCl₂+2e⁻.

DRI may specifically be used as the anode material in an all-Fe battery,where Fe is the reactive species at both the anode and cathode. In suchan embodiment, the DRI may serve as a solid metallic Fe anode at 100%SOC, and the anode will form a soluble Fe′ species (i.e., FeCl₂) upondischarge. The cathode active material may be a soluble inorganicFe-based salt, such as the FeCl₂/FeCl₃ redox couple. The cathode activematerial may also be an inorganic- or organic-based coordinationcompound, such as K₃Fe(CN)₆. At the cathode, the soluble Fe species willundergo redox reactions associated with the Fe²⁺/Fe³⁺ redox couple. Onespecific example of an all-Fe battery employing DRI as the activematerial would utilize DRI as the anode material with an electrolytecontaining concentration HCl (1-5 M). At the anode, the DRI would engagein the following half-cell reaction upon discharge: Fe+2Cl⁻→FeCl₂+2e⁻.At the cathode, soluble FeCl₃ would undergo the following half-cellreaction upon discharge: 2FeCl₃+2e⁻→2FeCl₂+2Cl⁻. The full cell reactionupon discharge would be Fe+2FeCl₃→3FeCl₂. The DRI may be used as afeedstock for the soluble FeCl₂ required in solution to enable thecathode reaction by allowing the DRI to react with HCl in solution, willengage the following spontaneous chemical reaction: Fe+2HCl→FeCl₂+H₂.

In some embodiments, DRI is used as the anode in a flow battery, inwhich DRI pellets are transported from a storage tank through anelectrochemical reactor where the DRI pellets react electrochemically.The DRI pellets remain in electrical contact with one another as theyflow through the electrochemical reactor, enabling sufficient electricalpercolation to provide high electrical conductivity through thecollection of pellets. The electrolyte may be acidic (pH<5), neutral(5<pH<9), or alkaline (pH>9). In specific embodiments, the dischargereactions may proceed such that the metallic Fe anode forms a solubleproduct (e.g., FeCl₂) upon discharge, or a sparingly soluble (e.g.,Fe(OH)₂) discharge product film on the surface of the transported DRIpellets. Specific embodiments concerning methods of transporting the DRIpellets through the battery include any of methods known in the art fortransporting particulate matter or slurries or suspensions, includingwithout limitation transport by pressure-driven fluid flow, using afluidized bed, by mechanical conveyor such as a conveyor belt, rotatingdrum, or using a helical screw. In some embodiments, the mechanicalconveyor or screw comprises an electronically conductive material suchas a metal or carbon that also serves as a current collector of thebattery.

In various embodiments, DRI is used as a feedstock source of metallic Fein the synthesis of FeCl₂ according to the following spontaneouschemical reaction: Fe+2HCl→FeCl₂+H₂. The DRI may be used as a feedstockmaterial as pellets, or pellets may be crushed into a powder. Further,DRI fines (pellet or particle size <0.5 cm), which are a waste productof the DRI process, could be used as the feedstock material. Iron iodide(FeI₂) and iron bromide (FeBr₂) can be synthesized in an analogousfashion, where HI and HBr would be substitute acids for HCl in the saltsynthesis.

In various embodiments, DRI is used to form a packed catalyst bed forgas-phase or liquid-phase reactions. In some embodiments, a packedcatalyst bed of DRI may be used as a catalyst in the Haber-Bosch processfor the production of ammonia. The DRI may replace, or may be used inaddition to, iron powder, which is typically used in the Haber-Boschprocess. In particular, the wustite coating that exists incommercially-produced DRI may be desirable for promoting reactions inthe Haber-Bosch process. In some embodiments, the iron or iron saltcomponent of the DRI, which may be iron oxide, hydroxide, or carbide, isreacted with another constituent such as another metal or metal salt toform a catalytically-active surface on the DRI. DRI may be used as afeedstock to produce alkali ferrocyanide salts. First, DRI can be usedto synthesize FeCl₂ according to the following spontaneous chemicalreaction: Fe+2HCl→FeCl₂+H₂. Subsequently, the FeCl₂, derived from DRI,can be used to synthesize Na₄Fe(CN)₆.10H₂O according to the followingreactions: Calcium ferrocyanide synthesis: 6 HCN+FeCl₂+3Ca(OH)₂→Ca₂Fe(CN)₆.11H₂O+CaCl₂; Conversion to mixed salt:Ca₂Fe(CN)₆.11H₂O+2 NaCl→CaNa₂Fe(CN)₆.11H₂O (s)+CaCl₂ (aq); andConversion to Na salt: CaNa₂Fe(CN)₆.11H₂O+Na₂CO₃→Na₄Fe(CN)₆.10H₂O+CaCO₃.In this conventional Na₄Fe(CN)₆.10H₂O synthesis processes, FeCl₂(˜$0.2/mol) represents ˜54% of the overall raw materials cost.Therefore, replacing FeCl₂ with DRI (˜$0.01/mol) has the potential tosignificantly cut the raw materials cost of Na₄Fe(CN)₆.10H₂O by half.

In various embodiments, DRI is used as an electrode for the hydrogenevolution reaction (HER) for the production of hydrogen (H₂) gas viaelectrolysis. The DRI may be used as a catalytic surface to promote theHER, or as a conductive substrate for one or more other catalystmaterials. In the substrate embodiment, the DRI may be coated in acontinuous layer of catalyst material or decorated with catalystparticles. Platinum (Pt) metal is an example of a catalyst that may beused to coat or decorate a DRI substrate for the HER. DRI may be usedfor the HER in either acidic or alkaline solutions.

In various embodiments, porous DRI pellets is used as an OER electrode.Non-limiting examples of the way in which DRI may be used for thispurpose include: in the as received state, after electroplating surfacewith a transition metal, after electroless plating surface with atransition metal, after the surface is modified through chemicaletching, after surface modifications through thermal processing, orafter OER catalyst is thermally imparted onto the DRI substrate surface.

In various embodiments, DRI is used as an electrode for the oxygenevolution reaction (OER) for the production of oxygen (O₂) gas viaelectrolysis. Non-limiting ways in which the DRI can be used include asa catalytic surface to promote the OER, or as a conductive substrate forone or more other catalyst materials. In embodiments where the DRI is asubstrate, the DRI may be coated in a continuous layer of catalystmaterial or decorated with catalyst particles. Nickel (Ni) metal is anexample of a catalyst that may be used to coat or decorate a DRIsubstrate for the OER. DRI may be used for the OER electrode in eitheracidic or alkaline solutions. DRI may be used as a catalyst or electrodesubstrate in alkaline electrolyzers.

In another embodiment, DRI is used in an oxygen reduction reaction (ORR)electrode. In some embodiments, the iron or iron salt component of theDRI, which may be iron oxide, hydroxide, or carbide, is reacted withanother constituent such as another metal or metal salt to form an ORRcatalyst. This catalyst may form on the surface of a DRI pellet or maypenetrate into the DRI pellet, and may be a portion of or substantiallytransform the entirety of the DRI. DRI fines as well as DRI pellets orcrushed pellets may be used as an ORR electrode. In some embodiments,the ORR catalyst formed from the DRI is a mixed metal oxide comprisingiron. In other embodiments, the ORR catalyst is an oxide that comprisesiron and another transition metal. In various embodiments, the ORRcatalyst is a spinel structure oxide that comprises iron and manganese.

In various embodiments, a packed bed of DRI is used in a waterfiltration device. In such an embodiment, the DRI may be housed in acolumn, creating a packed bed of DRI pellets. Particulate matter istrapped within the pores inside DRI pellets and within the void spacebetween DRI pellets. Use of pelletized iron as the filtration medium mayprovide the ability to tune the pressure drop and filtrationeffectiveness.

In various embodiments, DRI is used as a metallic iron feedstock for theproduction of Fe-containing industrial or specialty chemicals, such as:ferrocyanides, iron tris-bipyridine, and ferrocene, among others.

FIG. 1 is a schematic view of a battery (or cell) 100, according tovarious embodiments of the present disclosure. Referring to FIG. 1 , thebattery 100 includes a vessel 101 in which an air electrode 103, anegative electrode 102, a liquid electrolyte 104, and a currentcollector 106 are disposed. The liquid electrolyte 104 may separate theair electrode 103 from the negative electrode 102.

The negative electrode 102 may include metallic pellets 105 that maycomprise by elemental mass at least 50 wt % metal, such as at least 60wt % metal. In some embodiments, the metallic pellets 105 may compriseat least 60 wt % iron by elemental mass. Accordingly, the pellets 105may be referred to as iron-containing pellets. The pellets 105 may beelectrically connected to one another and may be disposed in one or morelayers to form the negative electrode 102. In various embodiments, thenegative electrode 102 may be a slurry. In various embodiments, theslurry may include one or more metallic pellets 105 therein. In variousembodiments, the slurry may include dissolved particles, such asparticles corresponding to the compositions of the metallic pellets 105as discussed herein. As a specific example, the negative electrode 102may be a slurry including iron. In various embodiments, the positiveelectrode 103 may be a slurry. In various embodiments, the negativeelectrode 102 may take the form of a gel. A flowable, semi-solidnegative electrode 102 (e.g., a flowable, semi-solid iron electrode,etc.) may be valuable for large-scale energy storage systems due to lowcost of manufacture and ease of assembly into cell architectures. Forexample, iron, in the reduced form, is highly conductive. By suspendingiron particles in a polymer gel, a percolating networking of ironparticles may be generated, thereby creating a conductive andelectroactive gel that may form the negative electrode 102. As examples,the polymer gel may be formed by dissolving organic polymers (e.g.,carboxymethyl cellulose (CMC)), or by dissolving an inorganic,oxide-forming network (e.g., SiO₂ dissolved in concentrated KOH). Incertain embodiments the electrolyte is gelled. In certain embodimentssilica (SiO₂) or other network forming oxides such as boron oxide (B₂O₃)or alumina (Al₂O₃) are dissolved in an alkaline liquid to form a gel. Incertain embodiments, a network-forming organic molecule is dispersed ina liquid electrolyte to form a gel electrolyte. In certain embodiments,the organic molecule comprises a polymer. In certain embodiments aliquid electrolyte is added to a solid polymer such as polyethyleneoxide (PEO), polyvinyl alcohol (PVA), polyacrylamide (PAM), orpolyacrylic acid (PAA) to form a gel electrolyte. Bio-derived polymers,such as cassava or gelatin, may also be used as the polymer additive. Incertain embodiments the gel electrolyte is formed in situ by dissolutionof silica (or other oxides) from DRI. In certain other embodiments,additional gel-former is intentionally added to a liquid electrolyte forpurposes of creating a gel. In certain embodiments a gel electrolyte isformed in situ due to the evaporation of solvent (e.g. water) from theelectrolyte, concentrating the dissolved salts and converting theelectrolyte from a liquid to a gel or supersaturated solution.

In various embodiments, the pellets 105 comprise one primary,iron-containing phase, and one or more secondary phases (“gangue”). Invarious embodiments, the oxidation state of the primary phase may rangefrom being highly reduced (e.g., metallic iron) to highly oxidized(e.g., ionic). For example, the pellets 105 may be substantiallymetallic iron, i.e. with a valence state of 0 (e.g. Fe⁰). Accordingly,in some embodiments, the pellet may comprise by mass at least 60 wt %metallic iron, preferably at least 80 wt % metallic iron, and in someembodiments, between 90 wt % and 98 wt % metallic iron. In various otherembodiments, the pellets 105 may be comprised of iron that is fullyoxidized to a 3+ valence state (e.g. Fe₂O₃). In various otherembodiments, the iron valence state may be between 0 and 3+. In variousembodiments, the primary phase may be an oxide, hydroxide, sulfide,carbide, or combinations thereof. For example, the primary phase mayhave a composition of Fe, FeO, Fe₂O₃, Fe₃O₄, FeO_(x)(OH)_(y), Fe₃C,FeS_(x), FeO_(x)S_(y), and/or FeO_(x)S_(y)H_(z). In some embodiments,the pellets 105 may comprise direct reduced iron (DRI) pellets and thepellets 105 may comprise at least 60 percent of the total mass of thenegative electrode 102. In various embodiments, negative electrode 102may be composed of DRI pellets.

In various embodiments, the secondary phase comprises silicon. Forexample, the secondary phase may comprise silica (SiO₂) and/or one ormore silicates such as feldspar, mica, amphibole, pyroxene, olivine,tourmaline, and/or forsterite. In various other embodiments, thesecondary phase may include titanium, vanadium, manganese, magnesium,calcium, phosphorus, carbon, aluminum, zirconium, or any combinationthereof.

The pellets 105 may be spherical, as shown in FIG. 1 . For example, invarious embodiments, the pellets 105 may have an average diameterranging from about 0.5 mm to about 10 cm, such as about 10 mm. As aspecific example, the pellets 105 may have an average diameter of 4 mmto 20 mm. As used herein, the term “spherical” is used to describe anyrounded form that resembles a three-dimensional object with all itssurface points equidistant from its center, but in which all surfacepoints may not actually be equidistant from the center. Stated anotherway, “spherical” encompasses shapes that are perfect spheres and shapesthat may have the general appearance of a sphere by may not be perfectspheres, e.g., a ball. However, the present disclosure is not limited toany particular pellet shape. For example, pellets may bebriquette-shaped, as discussed below with regard to FIG. 2A.Additionally, while illustrated as whole pellets, the pellets 105 may bepieces of crushed pellets. For example, received pellets may be crushedand the pieces of those crushed pellets may form the pellets 105 in thenegative electrode, such as the pellets 105 packed into a bed. Invarious embodiments, the crushed pellets may have an average particlesize between 10 nm (nm=10⁻⁹ m) and 10 mm (mm=10⁻³ m), such as between10-100 nm, 1-100 um (um=10⁻⁶ m), or 1-10 mm. In some embodiments, thecrushed pellets may include a combination of pellets having differentaverage particle sizes.

In various non-limiting embodiments, the pellets 105 may have aninternal porosity ranging from about 2% to 80%, such as from about 50%to about 75%. In various non-limiting embodiments, the negativeelectrode 102 may have a pellet packing density in the range of about40% to about 74%. Accordingly, the liquid electrolyte 104 may infiltratethe spaces between the pellets 115 to impregnate the negative electrode102. To assure good conductivity through the pellets 105, low contactresistance may be required. In various embodiments, compression of thepellets 105 of the negative electrode 102 may ensure contact of thepellets 105. In various embodiments, the pellets 105 may have acompressive strength from between about 700 psi and about 2500 psi. Insome embodiments, such compressive strength pellets 105 may be placed ina bed constituting the negative electrode 102 and compressive force maybe applied to the pellets to improve conductivity.

The liquid electrolyte 104 may comprise an electropositive element, suchas Li, K, Na, or combinations thereof. In some embodiments, the liquidelectrolyte 104 may be basic, namely with a pH greater than 7. In someembodiments the pH of the electrolyte 104 is greater than 10, and inother embodiments, greater than 12. For example, the electrolyte 104 maycomprise a 6M (mol/liter) concentration of potassium hydroxide (KOH). Incertain embodiments, the electrolyte 104 may comprise a combination ofingredients such as 5.5 M potassium hydroxide (KOH) and 0.5M lithiumhydroxide (LiOH). For iron materials, high pH beneficially promotesmechanical stability, as iron is sparingly soluble in high pH liquids.In various embodiments, the pH is greater than 10, or greater than 12,or greater than 14 to ensure this low solubility of iron. By contrast,at low pH, such as pH less than 5, or pH less than 3, or pH less than 2,iron is soluble and the pellets would dissolve.

In various non-limiting embodiments, the negative electrode 102 may havea thickness in the range of about 0.5 cm to about 50 cm, such as fromabout 0.75 cm to about 25 cm. The pellets 105 may be arranged in thenegative electrode 102 at a packing density in the range of about 30% toabout 74%. In various non-limiting embodiments, the pellets 105 may bedisposed on one another (such as by dispersing or spreading, as in a bedof gravel), or may be mechanically attached or connected to one anotherby a process such as compaction or pressing. In other embodiments, thepellets 105 may be physically connected by a process such as welding orbrazing. In other embodiments, the pellets 105 may be joined to oneanother by arc welding. In other embodiments, the pellets 105 may beconnected by a combination of such connecting processes. In otherembodiments, the pellets 105 may be attached and connected to oneanother by conductive wires strung through holes in the pellets 105. Theholes in the pellets 105 may introduce additional contact pointsthroughout not only the thickness of the pellet 105 bed that is thenegative electrode 102, but also through the thickness of a singlepellet 105. Once strung, the wires may be pulled tightly to enhanceinter-pellet 105 contact and may then be mechanically held in place by aconductive mechanical stopper, which in turn may be connected to alarger current collector plate, such as current collector 106. In someembodiments, pellets 105 may be packed into a bed, optionally with theassistance of mechanical pressure applied by ahigh-temperature-resistant material, and then sintered in anon-oxidizing atmosphere. The result is a bed of pellets 105 that arefused together with low inter-pellet 105 contact resistance. Thesintered bed of pellets 105 may form the negative electrode 102.

In various embodiments, the pellets 105 may be produced from iron orepellets, such as taconite or magnetite or hematite. In variousembodiments, the pellets 105 may be produced by reducing iron orepellets to form a more metallic (more reduced, less highly oxidized)material, such as iron metal (Fe⁰), wustite (FeO), or a mixture thereof.In various non-limiting embodiments, the pellets 105 may be reducedtaconite, direct reduced (“DR”) taconite, direct reduced iron (“DRI”)pellets, or any combination thereof.

In various non-limiting embodiments, the pellets 105 comprise thecementite form of iron (Fe₃C). While iron batteries require aniron-containing starting material, the cementite form of iron (Fe₃C) maybe easier or cost less to acquire or transport. In various embodiments,cementite (Fe₃C) may be used as a starting electrode material for aniron-containing battery. For example, the pellets 105 may initially beformed of cementite (Fe₃C). The cementite (Fe₃C) may be convertedinitially to magnetite before or during early operation of the battery100, and the magnetite may be reversibly cycled between other ironoxidation states in order to store energy. The conversion to magnetitemay occur in the battery 100 in either case, and may not be performedexternally before assembling the battery 100. The cementite (Fe₃C)starting pellet 105 may take the form of an ore pellet of majoritycementite (Fe₃C) and/or as a formed pellet of majority cementite (Fe₃C)powder. In various embodiments, by treating the pellets 105 of a lowspecific surface area cementite material as the anode of the battery 100and discharging the battery 100 at current densities of about 25 mA/g, ahigh specific surface area iron oxide phase may be created. This highspecific surface area iron oxide phase may be used as the negativeelectrode 102.

Commercially available DRI pellets may not necessarily have optimalchemical and physical properties for maximizing electrochemicalperformance. In various embodiments, ex-situ treatments are performed onthe DRI pellets prior to assembly of the DRI pellets into the negativeelectrode 102. Various embodiments include processing DRI pellets withmechanical, chemical, and/or thermal processes before introducing theDRI pellets into the electrochemical cell (i.e., processing the DRIpellets ex-situ) to achieve better chemical and physical properties.Better chemical and physical properties may include higher content ofdesirable impurities (e.g., hydrogen evolution reaction (HER)suppressants), lower content of undesirable impurities (e.g., HERcatalysts), higher specific surface area, higher total porosity,different pore size distribution (e.g. multimodal to reduce masstransport resistance), different pellet size distribution (e.g.multimodal to enhance bed packing), different aspect ratio (e.g. toenhance bed packing), etc. Mechanical processes that may be applied tothe DRI pellets ex-situ may include crushing, pulverizing, and/orpowderizing. Thermal processes that may be applied to the DRI pelletsex-situ may include processing the DRI pellets in at elevatedtemperature in reducing (e.g., hydrogen), oxidizing, and/or carburizing(e.g., carbon monoxide and/or carbon dioxide) atmosphere. Chemicalprocesses that may be applied to the DRI pellets ex-situ may includeacid etching, etc. In various embodiments, to increase accessiblecapacity of the DRI pellets during the discharge reaction, the DRIpellets may be pretreated by soaking in an acid bath (e.g., concentratedHCl) that will etch the iron and enlarge pores in the DRI pellets,increasing the total porosity of the DRI pellets in comparison to DRIpellets not etched in an acid bath. After pretreatment, the etched andnow porous DRI pellets may be assembled into the negative electrode 102.The etch time may be optimized to increase the usable capacity of a DRIpellet, without losing too much active material to the acid etchingsolution. In various embodiments, DRI may be used as an electrode in anelectrochemical cell and may be charged with current. This process mayincrease the surface area of the DRI.

The current collector 106 may be in the form of a conductive plateelectrically connected to the negative electrode 102. However, thecurrent collector 106 may have other configurations, as discussed belowwith regard to FIG. 2A.

The positive electrode half-reaction, as occurring on discharge at theair electrode 103 in an alkaline electrolyte, may be O₂+4 e⁻+2H₂O→4 OH⁻;the corresponding half reaction occurring at the negative electrode 102,starting from a fully metallic iron (fully charged negative electrode)may be 2Fe→2Fe²++4e⁻, giving a net discharge reaction of 2Fe+O₂+2H₂O→2Fe(OH)₂. In various embodiments, oxygen may be delivered to the airelectrode 103. This delivery of oxygen to the air electrode 103 may bedone in forms other than gaseous oxygen, including oxygen containingcompounds in gaseous, liquid, or solid states.

Various configurations of starting materials are possible, with a rangeof iron valence states (0 to 3+) and counter-ions O²⁻, OH⁻, S²⁻, etc.For example, other possible discharge products include Fe₂O₃, Fe₃O₄,FeO, FeOOH, FeS, FeS₂, etc., and combinations thereof.

In various embodiments, the packing of the pellets 105 in a bed to formthe negative electrode 102 may create macro-pores in between individualpellets 105. Additionally, in various embodiments, the individualpellets 105 may each have a porous, e.g., micro-porous surface. Themicro-pores in the surface of the pellets 105 may provide a greatersurface area for each individual pellet 105 than if the pellet 105 werea smooth sphere. The pore size of the pellets may vary. In someembodiments, the pellet 105 may have a volume weighted mean pore size ofgreater than 1 micron, such as 1 micron to 10 microns, etc. The poresize distribution within the pellet may be measured by mercury intrusionporosimetry. Mercury intrusion porosimetry is a technique in which apressurized chamber is used to force mercury into the pores of a pellet.The mercury is forced into larger pores first, and as the chamber isincreasingly pressurized, the mercury is forced into smaller and smallerpores. A physical relation such as the Washburn equation may be used torelate the applied pressure to the pore size, resulting in a volume- orarea-weighted pore size distribution. The pore size distributions may betransformed into cumulative distributions, from which the valuesd_(pore, 90% volume) and d_(pore, 50% surface area) may be deduced asstated in Tables 1, 2, and 3 discussed above.

FIG. 6 is a schematic view of the battery 100 showing expanded views ofthe macro-pores 602 and micro-pores 604 according to various embodimentsof the present disclosure. The macro-pores 602 are created by the gapsin-between individual pellets 105 when the pellets 105 are packed into abed. The macro-pores 602 may facilitate ion transport through a verythick (e.g., multi-centimeter) electrode 102. The micro-pores 604 may bedeformations in the surface of the pellets 105 themselves. Themicro-pores 604 may allow high surface area active material to be incontact with electrolyte 104 to enable high utilization of the activematerial via a solid-solid electrochemical reaction. The micropores mayinclude cracks in the pellet. Such cracks may be formed during theproduction of the pellet, or may be introduced afterwards, such as byapplying a mechanical load that causes cracking. This electrodestructure with macro-pores 602 and micro-pores 604 lends itselfspecifically to improving the rate capability of extremely thickelectrodes for stationary long duration energy storage, where thickelectrodes may be required to achieve extremely high areal capacities.

FIG. 7 illustrates a single pellet 105 of the battery 100. The pellet105 may include micro-pores 604 in the solid phase surface 702 of thepellet 105. The electrolyte 104 may fill the micro-pores 604 therebygiving the outer surface area of the sphere that is the pellet 105 bothliquid phase electrolyte areas associated with the micro-pores 604 andsolid phase areas surface 702. The filling by electrolyte of themicro-pores 604 reduces the solid phase areas where the surface 702contacts the electrolyte to the external surface of the pellet, givingthe pellet 105 a low effective specific surface area (e.g., low m²/g)which reduces electrolyte concentration boundary layers on the solidphase surfaces 702. Many metal anodes (e.g., Zn, Fe, Al) in aqueousbatteries are known to undergo self-discharge due to spontaneousreaction with the electrolyte, forming an oxidized metal and hydrogengas. For long duration energy storage systems (e.g., systems withdischarge durations of 8 hours or greater, such as 8 to 20 hours, 20 to24 hours, 24 hours or greater, etc.), self-discharge may limitperformance since cells may self-discharge a significant fraction of thestored capacity before a complete discharge cycle is finished. In someembodiments, metal electrodes with low specific surface area (e.g., lowm²/g) are used to suppress self-discharge in low-rate, long durationenergy storage systems. In many typical, modern electrochemical cells,high specific surface area is desirable to promote high rate capability(i.e., high power) through the introduction of many surface sites forreactions to take place. In long duration systems, the rate capabilityrequirement is significantly reduced, so low specific surface areaelectrodes may meet target rate-capability requirements while minimizingthe rate of self-discharge.

In various embodiments, an electrolyte 104 additive that forms a thin,passivating film (e.g., Na₂MoO₄), is added to the battery 100. In thismanner, self-discharge of the anode may be limited to only a small layeron the surface of the anode. This passivating film will limit the extentof the self-discharge reaction. To recover reactivity of the metalanode, a short and aggressive charging pulse can reduce the surfacefilm. Once the surface film is reduced, the discharge reaction canproceed.

In various embodiments, resistive elements are intentionally introducedinto the battery 100 to enable slow charging. By increasing theeffective resistance of other cell components (i.e., not the negativeelectrode 102 or the negative current collector 106), a larger overallcell polarization can be achieved. Doing this may cause the negativeelectrode 102 to have larger polarization. If the extra negativeelectrode 102 polarization is sufficiently large, the absolute potentialof the electrode 102 when it is an Fe electrode may become sufficientlylow to activate the Fe(OH)₂→Fe reaction at lower cell-level currents.This effect may be achieved by increasing the effective resistance ofthe electrolyte 104, cathode (e.g., electrode 103), or cathode currentcollector.

FIG. 2A is a schematic view of a battery 200, according to variousembodiments of the present disclosure. The battery 200 is similar to thebattery 100, so only difference therebetween will be discussed indetail.

Referring to FIG. 2A, the battery 200 includes a vessel 101 in which anair electrode 103, a negative electrode 102, a liquid electrolyte 104,and a current collector 106 are disposed. The liquid electrolyte 104 mayseparate the air electrode 103 from the negative electrode 102. Theliquid electrolyte 104 may also impregnate the negative electrode 102.

In various embodiments, the negative electrode 102 may includebriquette-shaped pellets 115. Herein, “briquette-shaped” may refer to arounded rectangular prism. For example, the pellets 115 may have alength ranging from 10 to 500 mm, a width ranging from 5 to 250 mm, anda thickness ranging from 5 to 200 mm. In some embodiments, the pellets115 may have a length of about 100 mm, a width of about 50 mm, and athickness of about 30 mm. In various non-limiting embodiments, thepellets 115 may have an internal porosity ranging from about 50% toabout 1%.

In various other embodiments, the pellets 115 may be formed of hotbriquetted iron (“HBI”), which may be formed by combining andaggregating pellets, or which may be formed by combining and aggregatinga powdered metal, such as powdered iron fines.

The current collector 106 may be formed of a conductive materialelectrically connected to the negative electrode 102. The currentcollector 106 may directly contact lower and side surfaces of thenegative electrode 102. In some embodiments, the current collector 106may optionally include projections 109 that extend through the negativeelectrode 102, so as to directly contact internal regions thereof. Theprojections 109 may also reduce the effective transport lengths withinthe electrode 102 from the total pellet bed thickness to theinter-projection 109 spacing. Additionally, these projections 109 may beused to affix a mechanical clamping mechanism to incorporate down-forceonto the pellet bed, while serving as a current collection element. Forexample, FIG. 2B illustrates an example plate 250 over the bed ofpellets 115 compressing the electrode 102. The plate 250 may be affixedto the projections 109 by clamps 252 attaching the plate 250 to theprojections 109 and causing the plate 250 to exert the compressing forceon the bed of pellets 115 that is the negative electrode 102. In thismanner, the plate 250 and clamps 252 may be a mechanical clampingmechanism. Similarly, the current collector may utilize magnets tocompress the material forming the negative electrode 102. For example,the plate 250 could be a magnet attracted to a bottom of the housing101, projections 109, and/or current collector 106 that may pull theplate 250 onto the pellets 115 to compress the bed of pellets 115 thatis the negative electrode 102. In some embodiments, the currentcollector 106, the projections 109, and/or another element in thebattery 200 may be magnetic and may pull the pellets 115 down and/ortogether to compact the bed of pellets 115. In some embodiments, thecurrent collector 106 may be a two part collector with a first partattached to a front face of the negative electrode 102 and a second partattached to a back face of the negative electrode 102. The front face ofan electrode may be the surface disposed generally toward theelectrolyte and the back face of an electrode may be the surfacedisposed generally away from the electrolyte. In some embodiments, thefirst part may be attached to the front face may be a porous structure(e.g., a mesh) and the second part attached to the back face may be asolid. Having the current collector on the front face of the electrodeand back face of the electrode may aid in applying a clamp force and mayenable more uniform reaction rates throughout the entire electrode. Thefront and back portions of the current collectors may be short circuitedtogether to impact reaction rate distributions. In some embodiments, thecurrent collector 106 may clamp onto the negative electrode 102.

In a metal-air battery, pelletized and briquetted electrode materialshave various advantages including high surface area, large internalporosity, and high electronic conductivity. Further advantages includemore efficient methods of transport and handling, which aresubstantially simplified for pelletized and briquetted materials, ascompared to powdered materials. Further advantages include simplicity offabrication of the negative electrode. In some embodiments, theelectrode may be formed by dispersing or pouring the pellets into avessel or container. The combination of the high electronic conductivityof the materials and the weight of the pellets, which may be the resultof the high density of iron-rich materials, provides a low contactresistance between pellets.

The electrical conductivity of materials that may comprise the pelletsis generally ranked from high to low in the order: Femetal>FeO>Fe₃O₄>Fe₂O₃. However, the more reduced materials having higherconductivity also require greater input energy in processing, andtherefore, are more expensive and difficult to prepare. Thus, materialssuch as wustite and mixed phases containing some amount of iron metal,e.g. Fe/FeO, or Fe/Fe₃O₄, or Fe/Fe₂O₃, are generally preferred. Forexample, wustite (FeO) may provide a desired balance between inputenergy and processing cost versus electrical conductivity. As aspecific, but non-limiting example, pellets may be produced as reducedtaconite pellets, with a composition near FeO.

As one specific example, pellets may be largely spherical pellets ofmetallic iron, with a porosity of 50% (by volume) with a typicaldiameter of 10 millimeters (mm). A negative electrode may be 2centimeters (cm) thick, and may be formed of a packed bed of thepellets. In the case of hard packed spheres, it is known that thepacking density of randomly close-packed spheres may be approximately64%, and close packed spheres may reach 74% packing density. Thus, theoverall solid-phase density of a negative electrode may be approximately32% (50%×64%) to 39% (50%×74%). The negative electrode is infiltratedwith liquid electrolyte, comprised of 6M (mol/liter) concentration ofpotassium hydroxide (KOH).

Further advantages of the proposed negative electrode structures includethe existence of low-tortuosity electrolyte pathways in the interstitialspaces between the pellets, which allows for rapid liquid-phase ionictransport, and enables the use of thick, high areal capacity (>0.1Ah/cm²) metal negative electrodes. The disclosed concepts also allow forindependent tuning of the electrode surface area (that is, thesolid-liquid interface area) and the electrode porosity, as the pelletporosity and packing densities may be independently varied.

As a further advantage of the invention, pellets may be assembled byspreading and packing in a dry state. In other embodiments, pellets maybe first dispersed in a liquid electrolyte and then poured and spreadinto a battery vessel. In various embodiments, the vessel supporting thepellets may take various forms. While illustrated in FIGS. 1 and 2 as abed of pellets, the negative electrode 102 may have various differentshapes, such as a cone, tube, etc.

FIGS. 12A-12F are sectional views of exemplary batteries 1200A-1200Fhaving alternative electrode configurations including ordered arrays ofpellets 105. The batteries 1200A-1200F may be similar to the battery100, so only differences therebetween will be discussed in detail.

Referring to FIG. 12A, the battery 1200A may include one or more conicalcontainer 1202 supporting pellets 105. The conical container 1202 mayenable the self-alignment of the pellets 105. The conical container 1202may enable a modular design of the negative electrode 102 by having alarge “swimming pool” type of reactor with multiple conical containers1202 sitting on the bottom of the swimming pool of electrolyte 104. Theconical container 1202 may be a cost effective design for bed currentcollection.

Referring to FIG. 12B, the battery 1200B may include a container 101supporting an array of negative electrode pellets 105 that form anegative electrode 102. One or more positive electrodes 103 may beinserted into a negative electrode 102. The pellets 105 may beelectrically connected to one another and/or to a current collector 106.A separator 107 may surround and electrically isolate the positiveelectrodes 103 from the negative electrode 102.

As shown in FIG. 12C, the battery 1200C may positive electrodes 103 thatextend completely through an array of negative electrode pellets. In thebattery 1200C, the pellets 105 may be arranged into stacks alternatingwith the electrodes 103. Referring to FIG. 12D, the battery 1200D, thebattery 1200D is similar to the battery 1200C, except for omitting aseparator. In the battery 1200D, the pellets 105 may be arranged intosupported beds suspended in the electrolyte 104 along with theelectrodes 103.

FIG. 12E, illustrates another example battery 1200E, according tovarious embodiments of the present disclosure. In the battery 1200E, thepellets 105 may be arranged in a hexagonal array surrounding theelectrode 103 which may be circular in shape. FIG. 12F, illustratesanother example battery 1200F, according to various embodiments of thepresent disclosure. In the battery 1200F, the pellets 105 may bearranged in a hexagonal array surrounding the electrode 103 which may behexagonal in shape.

As discussed above, the pellets of the present disclosure are notlimited to any particular pellet shape. In various embodiments, thepellets may be iron agglomerates with various different shapes, such assintered iron agglomerate pellet 305 illustrated in FIG. 3A. Thesintered iron agglomerate pellets may have symmetrical and/ornon-symmetrical shapes. As an example, the sintered iron agglomeratepellets may have a symmetrical shape such as a sphere, ellipsoid,cylinder, or plate, or an irregular shape such as a granule. In variousembodiments, the sintered iron agglomerate 305 may be formed in afurnace, such as a continuous feed calcining furnace, a batch calciningfurnace, a shaft furnace, or any other type of furnace. As a specificexample, when the furnace is a continuous feed calcining furnace, thefurnace 307 may be configured with a rotating tube. In operation, ironpowder particles 302 may be feed into the furnace 307. The furnace 307may rotate and heat the iron powder particles 302 to sinter the ironpowder particles 302 together, thereby fabricating sintered ironagglomerate pellets, such as sintered iron agglomerate pellet 305. Thesintered iron agglomerate pellets, such as sintered iron agglomeratepellet 305, may provide the same chemistry and morphology of sinteredpellets discussed herein, such as pellets 105, 115, etc., and may besubstituted in the various embodiments for other shaped pellets. Thesintered iron agglomerate pellets, such as sintered iron agglomeratepellet 305, may include a neck 309 at the sintered joint of the ironpowder particles 302 joined together to form the sintered ironagglomerate pellets, such as sintered iron agglomerate pellet 305.

An advantage to using pellets formed as iron agglomerates is that themanufacture of such iron agglomerate pellets, such as sintered ironagglomerate pellet 305, may be less expensive than the manufacture ofspherical and/or briquette-shaped pellets, such as pellets 105, 115,etc.

In various embodiments, a sintered iron electrode, such as an entireelectrode and/or individual pellets, such as pellets 105, 115, 305,etc., may be formed from crushed precursors and/or byproduct materials(e.g., fines) from steel making processes (e.g., DRI). For example, DRIprecursors and DRI fines may be crushed, formed with a binder under heatand pressure, and then sintered to form a porous iron electrode in theshape of pellets 105, 115, 305, etc. and/or electrodes of other shapes,including but not limited to sheets, plates, bars, cylinders, and othershapes.

Various embodiments discussed below with reference to FIGS. 3B-3Dprovide for making sintered porous metal electrodes for batteries, suchas batteries 100, 200, 400, 800, 814, 900, 1000, 1100, and 1200described herein.

FIG. 3B illustrates one embodiment method 350 for making sintered porousmetal electrodes. The method 350 may include mixing metal and one ormore additives to form a green formed pellet in block 351 and sinteringthe green formed pellet to form a porous metal electrode in block 352.

Mixing metal and one or more additives to form a “green” formed pelletin block 351 may include hot pressing the mixture of the metal and theone or more additives to form the green formed pellet. In variousembodiments, the metal may include iron. In various embodiments, theadditives may include a combination pore former and binder additive. Asa specific example, a mixture of iron, polyethylene, and bismuth sulfidepowder may be hot pressed into a green formed pellet. In variousembodiments, the polyethylene may act as both a green forming binder anda pore former that is evaporated during the sintering step. Thepolyethylene may sublime at a temperature less than the sinteringtemperature. In various embodiments, other pore former additives that donot necessarily serve as a binder may be used, such as any inorganic ororganic material that is solid-phase at room temperature and liquid orgas phase between room temperature and the sintering temperature in anitrogen (e.g., N₂) atmosphere or argon/hydrogen (e.g., Ar(95%)/H₂ (5%)or other relative argon and hydrogen concentration) atmosphere. Invarious embodiments, multiple types of binders may be mixed together asadditives to the metal. Mixing of multiple types of binders may be usedto target specific microstructure morphologies and stabilize the powderbed during binder burnout.

Sintering the green formed pellet to form a porous metal electrode inblock 352 may include sintering the green formed pellet in a gasatmosphere at a time-temperature profile. The gas atmosphere may be anitrogen (e.g., N₂) atmosphere or argon/hydrogen (e.g., Ar(95%)/H₂ (5%)or other relative argon and hydrogen concentration) atmosphere. Invarious embodiments, the time-temperature profile may be a lineartime-temperature profile or a non-linear time-temperature profile. Forexample, the linear time-temperature profile may include a lineartemperature ramp-up period, followed by a constant soak temperatureperiod, followed by a linear ramp-down period. As a specific example,sintering the green formed pellet in a gas atmosphere at atime-temperature profile may include sintering the green formed pelletin a nitrogen (e.g., N₂) atmosphere or argon/hydrogen (e.g., Ar(95%)/H₂(5%) or other relative argon and hydrogen concentration) atmosphere,with a linear temperature ramp up to 850° C., soak at 850° C. for 15min, and linear ramp back down to room temperature. As another example,a non-linear time-temperature profile may have multiple ramps and soaksto better control the evaporation rate of the pore former, such as apolyethylene pore former. For example, the non-linear time-temperatureprofile may have a non-linear temperature ramp-up period, two or moresoak temperature periods with ramp-down and ramp-up periods in-between,and a non-linear ramp-down period.

FIG. 3C illustrates an embodiment system 360 for forming sintered porousmetal electrodes 362. The system 360 may include a continuous rollerfurnace having a series of heating elements 364 and belt 366 withrollers configured to convey items on the belt 366 through the furnacefrom one end to another while being heated by the heating elements 364.The area under the heating elements 364 may be configured to havecontrolled atmospheric conditions, such as an atmosphere of purehydrogen (H₂) supplied by hydrogen tank 369. The system 360 may includea powder supply 370, such as a hopper, container, drum, etc., thatsupports metal powder 371, such as iron oxide powder, etc., to be usedfor forming a sintered porous metal electrode 362. When the metal powder371 is iron oxide powder, the iron oxide powder may or may not beoxidized in air at high temperature, which would result in a fullyoxidized (Fe₂O₃) powder feedstock. The metal powder 371 may be depositedfrom the powder supply onto the belt 366 and compressed before being fedinto the furnace (i.e., under the heating elements 364). As examples,the metal powder 371 may be compressed by a slot die, compression roller372, press, or other compaction type device at the front of the furnace.The compressed metal powder may be fed by the belt 366 along the lengthof the furnace under the heating elements 364. As the metal powder 371is heated by the heating elements 364 in the hydrogen atmosphere whilebeing moved by the belt 366, H₂O vapor may be released from the metalpowder 371. The hydrogen reduces the iron oxide at elevated temperatureto form water and metallic iron (i.e., FeO_(x)+H₂→H₂O+Fe). The resultingmetal powder (e.g., iron powder) rolls on the belt 366 continuouslythrough the furnace, allowing the particles to sinter together, forminga sintered porous metal electrode 362 (e.g., a sintered porous Feelectrode) in a continuous fashion. In some embodiments, the sinteredporous metal electrode 362 may be cleaved into pieces once it exits thefurnace, such as by knife 378, pinch cleaver, cutting jet, or any othertype device configured to cut the sintered porous metal electrode 362into pieces. In some embodiments, the weight of the sintered porousmetal electrode 362 may break it into pieces.

FIG. 3D illustrates a system 380 for forming sintered porous metalelectrodes 362. The system 380 may be similar to the system 360described above, except that a metal sheet 382 may be placed under themetal powder 371 before the metal powder 371 is fed into the furnace. Inthis manner, the metal powder 371 may be sintered directly onto themetal sheet 382 thereby continuously forming sintered porous metalelectrodes 362 with integrated current collectors. The metal sheet 382may be a roll of metal being fed into the furnace under the metal powder371 and supporting the metal powder 371 on the belt 366. For example,the metal sheet 382 may be fed by a reel to reel system onto the belt366 before the metal powder 371 is deposited and compressed. In variousembodiments, the metal sheet 382 may be a metal foil. In variousembodiments, the metal sheet 382 may be formed of any metal selected toact as a current collector, such as nickel, iron, steel, etc.

FIG. 4 is a schematic of a battery 400 according to various embodimentsof the present disclosure. The battery 400 is similar to the battery100, so only differences between the batteries 100 and 400 will bediscussed in detail. The battery 400 may include spherical pellets 105disposed in a smaller particle composition, such as a composition formedfrom powdered metal feed stock, metal fines, metal grains, etc.

Long-duration electrochemical energy storage may benefit from verylow-cost material inputs. While the spherical pellets 105 of battery 100may provide extremely low-cost material, electrical and ionicconductivity through the spherical pellets 105 may not be ideal becauseof the limited points of contact inherent in touching spherical pellets105. One solution to providing better electrical and ionic conductivitymay be to use powdered metal feedstocks as an electrode, such as thenegative electrode 102. While powdered metal feedstocks used as anelectrode may provide for tailored electrical and ionic conductivity,powdered metal feedstocks may be high-cost to produce, especially incomparison to spherical pellets 105.

Various embodiments may provide a composite metal electrode architecturethat provides a lower cost than exclusively powdered metal feedstockelectrodes and/or higher electric conductivity than exclusivelyspherical pellet electrodes. As used herein, an average width ordiameter of the pellets is at least 10 times greater than an averagewidth or diameter of the powder particles in the powdered metalfeedstock. In various embodiments, the composite metal electrodearchitecture may include a mixture of spherical pellets and a smallermetal particle composition, such as powdered metal feedstock. Forexample, as illustrated in FIG. 4 , the negative electrode 102 mayinclude spherical pellets 105 disposed in smaller metal particlecomposition 402, such as a powdered metal feedstock. The sphericalpellets 105 and powdered metal feedstock as the negative electrode 102may provide a mixture of larger and smaller particles akin to marbles insand or other combinations of relative particle size. In someembodiments, the macropores between the larger pellets comprise smallerpellets. The composite metal electrode formed from the spherical pellets105 and powdered metal feedstock may provide an electrode architecturewith a cost, electrical conductivity, and/or ionic conductivity that maybe highly-tunable. In some embodiments, the composite metal electrodemay be wetted with the liquid electrolyte 104. As the powdered metalfeedstock included in the composite metal electrode may be wetted, thecomposite metal electrode formed from the spherical pellets 105 andpowdered metal feedstock may have a lower iron to electrolyte ratio thanan electrode formed of exclusively spherical pellets 105. The powderedmetal feedstock 402 improves the electrical conductivity between thepellets 105 in the electrode 102, and also the total packing density ofthe electrode.

In various embodiments, the composite metal electrode architecture mayinclude a mixture of spherical pellets and a smaller metal particlecomposition, such as metal fines or shavings. For example, asillustrated in FIG. 4 , the negative electrode 102 may include sphericalpellets 105 comprised of taconite and a smaller metal particlecomposition 402 comprised of conductive DRI fines. By combining low costtaconite pellets used as a bulk iron feedstock for the pellets 105 andwaste, conductive DRI fines as the smaller metal particle composition402, the cost of forming a conductive electrode upon assembly of thebattery 400 may be lowered. As other examples, the composite metalelectrode architecture may include a mixture of different sized iron oreparticles, such as larger iron ore pellets (e.g., taconite, DRI, spongeiron, atomized iron, etc.) and a smaller metal particle composition,such as metal fines or shavings (e.g., fines or shavings of DRI,taconite, sponge iron, atomized iron, etc.).

In some embodiments, the electrical conductivity of the metal electrodeis increased by adding conductive fibers, wires, mesh, or sheets to thepellets such that the conductive material is dispersed betweenindividual pellets.

Various embodiments provide for on-site synthesis of active materialsfor bulk energy storage systems using renewable energy over-production.In various embodiments, chemical costs may be reduced by configuring theenergy storage plant including an embodiment battery, such as anembodiment metal-air electrochemical cell discussed herein, for dualuse. The initial use of the energy storage plant may be to synthesizecritical active materials, such as metallic pellets, such as pellets105, 115, 305, etc., on site using much lower cost input chemicals andvery cheap or free renewable energy. The next use of the energy storageplant may be as an actual energy storage plant where the chemical(s)that were synthesized are the active materials, such as metallicpellets, such as pellets 105, 115, 305, etc. For example, a metal powderthat will ultimately be used in a very large battery may be synthesizedon site at the dual use energy storage plant prior to the batterycommissioning, for example by direct reduction using hydrogen that isgenerated electrochemically through alkaline or PEM electrolysis poweredby a renewable source (e.g., wind, solar, etc.) on site. This onsiteproduction of active materials in a first stage may not only lower thecost of production but also potentially avoid shipping costs. Inembodiments where iron ore is the source of the active material,renewable energy may be used to provide the thermal energy to reduce theore at the dual use energy storage plant. Additionally, renewable energyand may optionally be used to produce hydrogen as a reducing gas toreduce the ore. The ore or reduced ore may be optionally in the form ofiron containing pellets.

In various embodiments, metallic pellets, such as pellets 105, 115, 305,etc., may be synthesized in a first stage of a dual use energy storageplant and used in the negative electrode in a second stage of the dualuse energy storage plant. FIG. 5 illustrates an embodiment method 500for on-site synthesis of active materials, such as metallic pellets,such as pellets 105, 115, 305, etc., for bulk energy storage systemsusing renewable over-production. In block 501, during a first stage ofoperation, the dual use energy storage plant may be operated to produceactive materials, such as metallic pellets, such as pellets 105, 115,305, etc. For example, when iron ore is the source of the activematerial, the ore may be reduced on site at the dual use energy storageplant to synthesize metallic pellets, such as pellets 105, 115, 305,etc. In block 502 during a second stage of operation, the dual useenergy storage plant may use the active materials for long-durationenergy storage. For example, the synthesized metallic pellets, such aspellets 105, 115, 305, etc., may be loaded (or otherwise deposited,added, formed, etc.) into negative electrodes, such as electrodes 102,etc. of a battery, to support long-duration energy storage by the dualuse energy storage plant. In various embodiments, the operations ofblocks 501 and/or 502 may be performed using renewable energy.

FIG. 8A is a schematic of a battery 800 according to various embodimentsof the present disclosure. The battery 800 is similar to the battery100, so only differences therebetween will be discussed in detail. Thebattery 800 may be configured to flow electrolyte 104 over the negativeelectrode 102. For example, the battery 800 may include a circulatingpump 802 and piping configured to enable the pumping of electrolyte 104at a selected rate, such as a constant flow rate, variable flow rate,etc., over the pellets 105 comprising the electrode 102. Transport ofelectrolyte 104 through a very thick (multi-centimeter) batteryelectrode 102 comprised of active material pellets 105 may bechallenging. Low electrolyte 104 transport rates can increaseoverpotential losses in the pellet 105 based electrode 102. By flowingelectrolyte 104, through the thick electrode 102, convective transportmay be introduced which promotes flow of electrolyte to individualpellets 105. As discussed above, pellets 105 may be micro-porous and thereaction condition can benefit by decreasing electrolyte 104concentration boundary layers that may arise through the thickness ofthe entire pellet 105 bed of the electrode 102 and through macro-pores,such as macro-pore 602, in the pellet 105 bed. The electrolyte 104 flowwill generally decrease overpotential losses by homogenizing theelectrolyte 104 composition throughout the macro- and micro-structure ofthe electrode 102. Electrolyte 104 flow rates may be preferably chosento be low enough that any energy consumed by pumping does not consumeundesirable amounts of energy. In various embodiments, the electrolyte104 flow rate may be a steady flow rate or a variable flow rate.

In various embodiments, by flowing electrolyte 104 at a low, butconsistent flow rate through the battery electrode 102 (e.g., thebattery electrode 102 comprised of active material pellets 105)convective transport may be introduced which promotes flow ofelectrolyte 104 to individual pellets 105. Pellets 105 may bemicro-porous and the reaction condition may benefit by decreasingelectrolyte 104 concentration boundary layers that may arise through thethickness of the entire pellet 105 bed (e.g., through the electrode 102)and through macro-pores in the pellet 105 bed (e.g., in the electrode102). The electrolyte 104 flow may generally decrease overpotentiallosses by homogenizing the electrolyte 104 throughout the macro- andmicro-structure of the electrode 102.

In various embodiments, electrolyte 104 formulations may be differentfor the charge, discharge, and idle states of the battery 800. Flowingdifferent electrolyte 104 formulations into the battery 800 whenswitching between states may improve utilization, self-discharge, andHER simultaneously. For example, in the case of an electrolytemanagement system with continuous flow, there may optionally be anarbitrary number of distinct electrolyte formulation reservoirs, eachconnected to the electrochemical cell with separate flow controllers(e.g., three reservoir and flow controller combinations 805, 806, 807).During different operation, different relative amounts of eachelectrolyte formulation could be flowed based on the optimalconcentrations of constituent species for the instantaneous operationmode (e.g., charge, discharge, idle). In some embodiments, theelectrolyte formulation may be adjust based on the instantaneous stateof charge of the battery 800. In various embodiments, a reservoir andflow controller combinations (e.g., 805, 806, 807) may be used to addadditional electrolyte 104 to the battery 800, for example therebycompensating for electrolyte 104 evaporation. In various embodiments,the battery 800 may include an overflow drain 820 or spill way passagethat may enable electrolyte 104 to overflow out of the battery 800. Forexample, the level of electrolyte 104 may be maintained because as thelevel of electrolyte 104 reaches the overflow drain 820, it may exit thebattery 800 to maintain the level of the electrolyte 104 at the overflowdrain 820 level.

FIG. 8B is a block diagram of an embodiment battery 814 including anadditive delivery system 815. The battery 814 is similar to the battery100, so only difference therebetween will be discussed in detail. In oneembodiment, the additive delivery system 815 may be a pump that deliversadditive-bearing liquid to the battery 814. In another embodiment, theadditive delivery system 815 may be a dry hopper that deliversadditive-bearing solids to the battery 814. As one example, the additivedelivery system 815 may be a sulfur delivery system. As a specificexample, when the additive delivery system 815 is a sulfur deliverysystem, the sulfur delivery system may be a pump that deliverssulfur-bearing liquid to the battery 814. In as another specificexample, when the additive delivery system 815 is a sulfur deliverysystem, the sulfur delivery system may be a dry hopper that deliverssulfur-bearing solids (e.g., polysulfide salts, iron sulfide (FeS),etc.) to the battery 814. In another example, the additive deliverysystem 815 may be a salt delivery system. Specifically, the additivedelivery system 815 may add certain solid-phase hydrogen evolutioninhibitors (e.g., Bi, Sb, As) as a soluble salt. For example, a solublesalt of a desired hydrogen evolution inhibitor, which dissolves toprovide in solution ions of the desired additive (i.e., Bi³⁺, Sb³⁺,As³⁺), may be added to the liquid electrolyte 104 by the additivedelivery system 815. The additive may be selected such that the redoxpotential of the inhibitor's ion-to-metal plating reaction (e.g.,Bi³⁺→Bi⁰) occurs at a higher half-cell potential (as measured vs. RHE(but at a lower cell potential)) than the potential of the chargingreaction of the anode active material. Thus, during charging of thebattery 800, the ionic form of the HER inhibitor may be electrodepositedonto the surfaces of the metal electrode, providing an inexpensive andsimple strategy for introducing an HER inhibitor to the battery 800electrolyte 104 chemistry. The electrodeposited inhibitor suppresses thehydrogen evolution reaction at the surface of the electrode, which maybe an electrode with open porosity. During the discharge mode, thedeposit may dissolve back into the electrolyte 104. The salt additivemay be preferably selected so that it does not degrade the operation ofthe cathode during charge or discharge operations. As another example,the salt added may be a carbonate salt. In some embodiments, theadditive delivery system 815 may deliver multiple additives to thebattery 800. For example, a combined additive composition such as acorrosion inhibitor that suppresses the HER reaction or suppressesself-discharge combined with an additive that improves capacityutilization may be delivered by the additive delivery system 815. Asanother example, an inhibitor that forms a passivation layer on themetal surface is paired with an additive that de-passivates the ironsurface and both may be delivered by the additive delivery system 815.In some embodiments, the additive delivery system 815 may deliveradditives comprising a molybdate ion. As an example, a molybdate ion maybe added via a molybdate compound such as KMoO₄. In one specificexample, the electrolyte 104 may include an additive concentration of 10mM molybdate anion. In other embodiments, the electrolyte 104 mayinclude additive concentrations ranging from 1-100 mM of the molybdateanion. In some embodiments, a surfactant additive may be delivered bythe additive delivery system 815. A surfactant additive may reduceelectrolyte surface tension and viscosity at the oxygen evolutionelectrode to generate smaller, uniformly sized, controllable bubblesduring charging. In one non-limiting example, 1-Octanethiol is added tothe alkaline electrolyte 104 at a concentration of 10 mM. In someembodiments, a corrosion inhibitor additive may be delivered by theadditive delivery system 815. In some embodiments, the additive deliverysystem 815 may delivery liquid and/or interphase interface inhibitors.In some embodiments, the additive delivery system 815 may deliveradditives as mixtures of solids. In some embodiments, the additivedelivery system 815 may deliver an electrolyte additive (e.g., Na₂MoO₄)that forms a thin, passivating film. Self-discharge of the anode istherefore limited to only a small layer on the surface of the anode.However, to recover reactivity of the metal anode, a short andaggressive charging pulse may be used to reduce the surface film. Oncethe surface film is reduced, the discharge reaction may proceed.

FIG. 8C is a block diagram of a battery system 850 including a series ofembodiment batteries 800 fluidly connected (or otherwise in liquidcommunication) according to various embodiments. The batteries 800 maybe arranged in a cascade manner such that overflow electrolyte 104 fromone battery 800 via its overflow drain 820 can flow into the nextbattery 800, establishing “liquid communication” between the batteries800. Linking these batteries 800 in series allows one source to supplyliquid electrolyte 104 to several batteries 800 simultaneously. Forexample, a single electrolyte supply pipe 851 connected to a pump 802may supply electrolyte 104 to the first battery 800. The overflow ofelectrolyte from the first battery 800 may flow to the second battery800 and to the third battery 800. From the third battery 800, theelectrolyte may overflow into the return pipe 852 and be circulated bythe pump 802 back to the supply pipe 851. In this manner, overflow fromthe final battery 800 can be re-circulated to the first battery 800. Inthe system 850 that utilizes shared electrolyte 104, flowing in acascading fashion between batteries 800, attributes of the electrolyte104 can be monitored and treated at a central location for manybatteries, such as monitoring station 853. Electrolyte 104 mediation,such as performing compositional adjustments or adding components, inorder to mitigate issues related to electrolyte carbonation, electrolytedehydration, and the like, may be beneficially conducted at themonitoring station 853. The monitoring station 853 may be collocatedwith the collection structure for the circulating electrolyte 104, suchas the return pipe 852. As an example, the monitoring station 853 maycontrol the supply of electrolyte 104 from different reservoir and flowcontroller combinations (e.g., 805, 806, 807), a filtration device 860,and/or a reserve electrolyte supply tank 855. In various embodiments,the monitoring station 853 may be configured to monitor electrolytehealth. Electrolyte health may be monitored while the battery is inoperation in order to determine the appropriate time to replenish,replace, or treat the electrolyte 104. The feedback mechanism employedby the monitoring station 853 may be manual or automated. When themonitoring station 853 is an automated system, the electrolyte qualitymeasurement may be one input to a control loop such as aproportional-integral-derivative (PID) loop that adjusts electrolyteconstituent concentrations on a continuous basis. The electrolytequality measurement may be done ex-situ on a small aliquot of theelectrolyte 104, or may be done operando on the active electrolyte 104while the batteries 800 are in operation. One non-limiting method forassessing electrolyte health is to measure the electrical conductivityof the electrolyte. One mechanism of degradation is carbonation of theelectrolyte over time, due to CO₂ dissolution in the electrolyte fromair. For example, a conductivity probe is used to evaluate theconcentration of carbonate in the electrolyte. The conductivity probe isused to monitor the state of health of the electrolyte. Whileillustrated as part of a cascading system 850, the monitoring station853 may similarly be part of an electrolyte delivery system for a singlebattery, such as the electrolyte system of FIG. 8A. The monitoringstation 853 may control the release of electrolyte 104 from and/or tothe reserve electrolyte supply tank 852 to increase and/or decrease thevolume of electrolyte 104 in the system 850. The monitoring station 853may control the flow of liquid through the filtration device 860. Thefiltration device 860 may be configured to filter liquid flowed throughit, such as water, electrolyte 104, etc. and the monitoring station 853may control the flow of liquid into and out of the filtration device860. For example, the filtration device 860 may be a water filter, suchas the water filter 1400 illustrated in FIG. 14 . The water filter 1400may be a packed bed 1401 of DRI that may operate as a water filtrationdevice. In such an embodiment, the DRI may be housed in a column,creating a packed bed 1401 of DRI pellets 197. Particulate matter willbe trapped within the pores inside DRI pellets 197 and within the voidspace between DRI pellets 197 as water flows through the bed 1401. Usingpelletized iron as the filtration mechanism may enable the ability totune pressure drop and filtration effectiveness.

FIG. 9 is a schematic of a battery 900 according to various embodimentsof the present disclosure. The battery 900 is similar to the battery100, so only difference therebetween will be discussed in detail.Alkaline iron electrode batteries operate best with certain additives inthe electrolyte/cell. These may have a range of solubilities, and somemay have a most beneficial effect when intimately mixed with the solidelectrode. As illustrated in FIG. 9 , in various embodiments, pellets902 including additives may be mixed with active-material dominantpellets 105 such that the negative electrode 102 may be a blendedelectrode. The additive pellets 902 may be partially and/or entirelyformed from additives, e.g., an iron sulfur compound, such as FeS, FeS₂,etc. In various embodiments, the liquid electrolyte 104 may compriseadditives to suppress the hydrogen evolution reaction at the anode orcathode. These may be soluble or insoluble, and may include metalloidHER inhibitors such as bismuth, antimony, tin, boron, indium, gallium,selenium. Additives may plate from solution or change phase duringoperation, for example, starting in dissolved solution and laterprecipitating as solids.

FIG. 10 is a schematic of a battery 1000 according to variousembodiments of the present disclosure. The battery 1000 is similar tothe battery 100, so only differences therebetween will be discussed indetail. Interfacial resistivity between the current collector 106 andthe negative electrode 102 comprised of pellets 105 may be high due tothe spherical structure of the pellets 105 contacting the currentcollector 106 in battery 100. Due to this, the electrode 102 sees anincreased effective current density at the pellet contacts. In variousembodiments, adding a layer 1002 of powdered iron (Fe) to the electrode102 and current collector 106 interface as illustrated in battery 1000of FIG. 10 may decrease interfacial resistivity. In battery 1000, thelayer 1002 of powdered iron may be added at the bottom of the bed ofpellets 105 to reduce the interfacial resistivity. The layer 1002 ofpowdered iron may be configured to form an interface between the pellets105 and a current collector 106 of the battery 1000. The average widthor diameter of the pellets 105 is at least 10 times greater than theaverage width or diameter of the powder particles in the layer 1002.

FIG. 11 is a schematic of a battery 1100 according to variousembodiments of the present disclosure. The battery 1100 is similar tothe battery 100, so only differences therebetween will be discussed indetail. The battery 1100 may include a monitoring system comprising oneor more sensors connected (e.g., wirelessly or via a wire) to acontroller 1110 configured to monitor the state-of-charge (SOC) and/orstate-of-health (SOH) of the iron electrode 102. Monitoring the SOCand/or the SOH may be valuable for improving controls and healthmonitoring of the battery 1100.

Various embodiments may include one or more of various methods tomonitor a chemical and/or physical attribute of the negative electrode102 including using a Mossbauer spectrometer, using a charge coupleddevice (CCD) detector (e.g., a color camera, etc.), using a straingauge, using a temperature sensor, measuring ion concentration,measuring electrolyte level displacement, measuring pellet bed height,measuring pellet size, measuring battery 1100 cell mass, measuringmagnetic susceptibility, and using gas sensing. In various embodiments,a NiOH/NiOOH electrode, containing a carbon conductive additive and/orbinder, may be used as a quasi-reference electrode to monitor potential.These NiOH/NiOOH electrodes may be placed at a variety of locationsthroughout the electrolyte vessel to also monitor potentialdistributions throughout the system.

For example, the SOC and/or SOH may be monitored in-situ by one or morestrain gauges 1102 connected to the vessel 101. The one or more straingauges 1102 may be connected to the controller 1110 and may outputmeasurements of the strain on the vessel 101 to the controller 1110. Thecontroller 1110 may be configured to convert the strain measurements toSOC and/or SOH measurements.

As another example, the SOC and/or SOH may be monitored in-situ by aMossbauer spectrometer comprised of a gamma source 1103 and gammadetector 1104. The gamma source 1103 may output gamma rays through thebattery 1100 which may be detected by the gamma detector 1104. The gammasource 1103 may be connected to the controller 1110 and the controller1110 may control the gamma source 1103 to output gamma rays. The gammadetector 1104 may be connected to the controller 1110 and may outputmeasurements of the gamma rays to the controller 1110. The controller1110 may be configured to convert the gamma ray measurements to SOCand/or SOH measurements.

As a further example, the SOC and/or SOH may be monitored in-situ by oneor more CCD detectors 1105 (e.g., a color camera, etc.) connected to thecontroller 1110. The CCD detector 1105 may capture and output images ofthe negative electrode 102 to the controller 1110. The controller 1110may be configured to use the images to determine a SOC and/or SOHmeasurement. For example, the controller 1110 may be configured tocorrelate the color of the pellets 105 in the images to a SOC and/or SOHmeasurement. As another example, the controller 1110 may be configuredto measure the pellet 105 size from the image data and/or may beconfigured to measure the pellet 105 bed height from the image data.

As a further example, the SOC and/or SOH may be monitored in-situ by oneor more ultrasonic transducers 1106 connected to the controller 1110.The ultrasonic transducer 1106 may output sound wave measurements to thecontroller 1110. The controller 1110 may be configured to use the soundwave measurements to determine a SOC and/or SOH measurement. Forexample, based on the roundtrip time of the sound wave to the surface ofthe pellet 105 bed, changes in height in the pellet 105 bed may bedetermined by the controller 1110 and correlated with SOC and/or SOHmeasurements.

As a further example, the SOC and/or SOH may be monitored in-situ by oneor more ion sensing electrodes 1107 connected to the controller 1110.The ion sensing electrode 1107 may output ion measurements, such as ionconcentration, to the controller 1110. The controller 1110 may beconfigured to use the ion measurements to determine a SOC and/or SOHmeasurement.

As a further example, the SOC may be monitored in-situ by one or morethermocouples 1108 connected to the controller 1110. The thermocouple1108 may output temperature measurements to the controller 1110. Thecontroller 1110 may be configured to use the temperature measurements todetermine a SOC and/or SOH measurement.

As a still further example, the SOC and/or SOH may be monitored in-situby one or more gas sensors 1109 connected to the controller 1110. Thegas sensor 1109 may output gas measurements, e.g., specific particledetections, concentrations, etc., to the controller 1110. The controller1110 may be configured to use the gas measurements to determine a SOCand/or SOH measurement.

In various embodiments, the physical and/or chemical attributes of thebattery 1100, and more specifically the negative electrode 102, measuredby the various sensors 1102-1109 may be used by the controller 1110 todetermine control operations to take in regard to the battery 1100, suchas operations to ensure battery 1100 health based on the monitored SOCand/or SOH of the negative electrode 102.

FIG. 13A illustrates a battery 1300 according to various embodiments. Asan example, the battery 1300 is a static type battery that uses DRI. Insome embodiments, the battery 1300 is a non-flowing aqueous typebattery. In some embodiments, the battery 1300 may be a primary battery.In some embodiments, the battery 1300 may be a secondary battery. Insome embodiments, the battery 1300 may include DRI pellets 198 in oneelectrode 1302 and/or may include DRI pellets 199 in another electrode1306. While illustrated as both including DRI pellets 198, 199, in someconfigurations only one of the electrodes 1302 or 1306 may include DRIpellets 198, 199, respectively while in other configurations bothelectrodes 1302, 1306 may include DRI pellets 198, 199, respectively. Invarious embodiments, the electrodes 1302 and 1306 may be separated byelectrolyte 1304. In various embodiments, the battery 1300 may be asealed battery. In various embodiments, the battery 1300 may be an openbattery, such as a battery open air type battery. In variousembodiments, the DRI pellets 198 may be similar to the various DRIpellets (or other DRI type configurations) described herein, such as DRIpellets 105, 115, 305, etc.

In various embodiments, the electrode 1302 is an anode of the battery1300 and the electrode 1306 is a cathode of the battery 1300. In variousembodiments, DRI is used as a redox-active electrode material when thebattery 1300 is of primary or secondary type. In one embodiment, DRI(such as DRI pellets 198) is used as an anode active material when thebattery 1300 is a secondary battery. In another embodiment, DRI (such asDRI pellets 198, 199) is used as an electrode material with alkalineelectrolyte (pH>9). In one particular embodiment, when the battery 1300is an alkaline secondary battery, the battery 1300 may employ a nickelcathode. In this embodiment, DRI serves as the starting material for theanode of the Ni—Fe alkaline secondary battery 1300, and may be used inits as-received state or may be processed before use according to otherembodiments described herein. Other electrochemical couples(combinations of a cathode and an anode) for use when the battery 1300is an alkaline battery employing a DRI anode include iron/nickel (Fe/Nicell) or iron/silver (Fe/Ag cell). In various embodiments, DRI may serveas an anode active material when the battery 1300 is a primary orsecondary battery where the pH of the electrode spans the acidic(pH<5.5) or neutral (5.5<pH<9) regimes. As an example, DRI may be usedas the anode active material in the battery 1300 employing anelectrolyte containing hydrochloric acid (HCl) in the concentrationrange of 1-5 M. At the anode, the DRI may engage in the followinghalf-cell reaction upon discharge: Fe+2Cl⁻→FeCl₂+2e⁻.

DRI may specifically be used as the anode material when the battery 1300is an all-Fe battery, where Fe is the reactive species at both the anodeand cathode. In such an embodiment, the DRI may serve as a solidmetallic Fe anode at 100% SOC, and the anode will form a soluble Fe′species (e.g., FeCl₂) upon discharge. The cathode active material may bea soluble inorganic Fe-based salt, such as the FeCl₂/FeCl₃ redox couple.The cathode active material may also be an inorganic- or organic-basedcoordination compound, such as K₃Fe(CN)₆. At the cathode, the soluble Fespecies will undergo redox reactions associated with the Fe²⁺/Fe³⁺ redoxcouple. As one specific example, when the battery 1300 is an all-Febattery employing DRI as the active material, the battery 1300 mayutilize DRI as the anode material with an electrolyte containingconcentration HCl (1-5 M). At the anode, the DRI would engage in thefollowing half-cell reaction upon discharge: Fe+2Cl⁻→FeCl₂+2e⁻. At thecathode, soluble FeCl₃ would undergo the following half-cell reactionupon discharge: 2FeCl₃+2e⁻→2FeCl₂+2Cl⁻. The full cell reaction upondischarge would be Fe+2FeCl₃→3FeCl₂. The DRI may be used as a feedstockfor the soluble FeCl₂ required in solution to enable the cathodereaction by allowing the DRI to react with HCl in solution, will engagethe following spontaneous chemical reaction: Fe+2HCl→FeCl₂+H₂.

FIG. 13B illustrates a battery 1310 according to various embodiments.The battery 1310 is similar to the battery 1300 described above, exceptthat the battery 1310 is a flow battery using DRI. In variousembodiments, DRI pellets 198, 199, are transported from respectivestorage tanks 1311, 1312 through the electrodes 1302, 1306, respectivelyof the flow battery 1310 by one or more respective transport systems1314, 1316. As an example, DRI may serve as the anode in the flowbattery 1310 in which DRI pellets are transported from the storage tankthrough an electrochemical reactor where the DRI pellets reactelectrochemically. The DRI pellets remain in electrical contact with oneanother as they flow through the electrochemical reactor, enablingsufficient electrical percolation to provide high electricalconductivity through the collection of pellets. The electrolyte 1304 maybe acidic (pH<5), neutral (5<pH<9), or alkaline (pH>9). In specificembodiments, the discharge reactions may proceed such that the metallicFe anode forms a soluble product (e.g., FeCl₂) upon discharge, or asparingly soluble (i.e., Fe(OH)₂) discharge product film on the surfaceof the transported DRI pellets. Specific embodiments concerning methodsof transporting the DRI pellets through the battery 1310 via one or bothof the transport systems 1314, 1316 include any of methods known in theart for transporting particulate matter or slurries or suspensions. Forexample, one or both of the transport systems 1314, 1316 may be withoutlimitation pressure-driven fluid flow systems, a fluidized bed system,or a mechanical conveyor system, such as a conveyor belt, rotating drum,or a helical screw. In some embodiments, the transport systems 1314,1316, such as a mechanical belt, screw, drum, etc., comprises anelectronically conductive material such as a metal or carbon that alsoserves as a current collector of the battery 1310.

Various embodiments provide a method for making a sintered porous metalelectrode including mixing metal and one or more additives to form agreen formed pellet, and sintering the green formed pellet to form asintered porous metal electrode. In various embodiments, the methodincludes mixing the metal and the one or more additives to form thegreen formed pellet by hot pressing the mixture of the metal and the oneor more additives to form the green formed pellet. In variousembodiments, the metal comprises iron. In various embodiments, at leastone of the one or more additives is both a pore former and binderadditive. In various embodiments, the one or more additives comprise anadditive of polyethylene and an additive of bismuth sulfide powder. Invarious embodiments, at least one of the one or more additives is a poreformer additive and at least one other of the one or more additives is abinder additive. In various embodiments, the binder additive is amixture of two or more different type binders. In various embodiments,sintering the green formed pellet to form the sintered porous metalelectrode comprises sintering the green formed pellet in a gasatmosphere at a time-temperature profile. In various embodiments, thegas atmosphere is a N₂ atmosphere or an Ar/H₂ atmosphere. In variousembodiments, the gas atmosphere is a Ar(95%)/H₂ (5%) atmosphere. Invarious embodiments, the time-temperature profile comprises a lineartemperature ramp-up period, followed by a constant soak temperatureperiod, followed by a linear ramp-down period. In various embodiments,the linear temperature ramp-up period raises a temperature of the greenformed pellet to 850° C., a soak temperature is 850° C., and the linearramp-down period drops a temperature of the green formed pellet to roomtemperature. In various embodiments, the constant soak temperatureperiod is 15 minutes. In various embodiments, time-temperature profilecomprises a non-linear temperature ramp-up period, two or more soaktemperature periods with ramp-down and ramp-up periods in-between, and anon-linear ramp-down period.

Various embodiments may provide a method for making a sintered porousmetal electrode, including feeding compressed metal powder into acontinuous roller furnace, and passing the compressed metal powderthough the furnace to sinter the metal powder together to form asintered porous metal electrode. In various embodiments, the metalpowder comprises iron oxide powder. In various embodiments, the methodmay include compressing the metal powder before feeding the metal powderinto the furnace. In various embodiments, compressing the metal powdercomprises passing the metal powder through a slot die or under acompression roller. In various embodiments, the method may includeplacing a metal sheet under the powder before feeding the metal powderinto the furnace. In various embodiments, the metal sheet is receivedfrom a roll of metal being fed into the furnace and is supporting thecompressed metal powder in the furnace. In various embodiments, themetal sheet is a metal foil. In various embodiments, the metal sheetcomprises, nickel, iron, or steel. In various embodiments, the methodmay include cleaving the sintered porous metal electrode into sections.In various embodiments, the continuous roller furnace heats the metalpowder in an atmosphere of hydrogen. In various other embodiments thecontinuous roller furnace heats the metal powder in an inert atmosphereof nitrogen or argon. In various other embodiments the continuous rollerfurnace heats the metal powder in an atmosphere that comprises a mixtureof hydrogen, nitrogen, and/or argon.

Various embodiments may provide devices and/or methods for use in bulkenergy storage systems, such as long duration energy storage (LODES)systems, short duration energy storage (SDES) systems, etc. As anexample, various embodiments may provide batteries and/or components ofbatteries (e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000,1100, 1200, 1300, 1310, pellets 105, 115, 305, 198, 199, systems 850,etc.) for bulk energy storage systems, such as batteries for LODESsystems. Renewable power sources are becoming more prevalent and costeffective. However, many renewable power sources face an intermittencyproblem that is hindering renewable power source adoption. The impact ofthe intermittent tendencies of renewable power sources may be mitigatedby pairing renewable power sources with bulk energy storage systems,such as LODES systems, SDES systems, etc. To support the adoption ofcombined power generation, transmission, and storage systems (e.g., apower plant having a renewable power generation source paired with abulk energy storage system and transmission facilities at any of thepower plant and/or the bulk energy storage system) devices and methodsto support the design and operation of such combined power generation,transmission, and storage systems, such as the various embodimentdevices and methods described herein, are needed.

A combined power generation, transmission, and storage system may be apower plant including one or more power generation sources (e.g., one ormore renewable power generation sources, one or more non-renewable powergenerations sources, combinations of renewable and non-renewable powergeneration sources, etc.), one or more transmission facilities, and oneor more bulk energy storage systems. Transmission facilities at any ofthe power plant and/or the bulk energy storage systems may beco-optimized with the power generation and storage system or may imposeconstraints on the power generation and storage system design andoperation. The combined power generation, transmission, and storagesystems may be configured to meet various output goals, under variousdesign and operating constraints.

EXAMPLES

The following examples are provided to illustrate various embodiments ofsystems, processes, compositions, applications and materials of thepresent inventions. These examples are for illustrative purposes, may beprophetic, and should not be viewed as limiting, and do not otherwiselimit the scope of the present inventions.

FIGS. 15-23 illustrate various example systems in which one or moreaspects of the various embodiments are used as part of bulk energystorage systems, such as LODES systems, SDES systems, etc. For example,various embodiment batteries and/or components described herein (e.g.,any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200, 1300,1310, pellets 105, 115, 305, 198, 199, systems 850, etc.) may be used asbatteries and/or components for bulk energy storage systems, such asLODES systems, SDES systems, etc. As used herein, the term “LODESsystem” unless expressly used otherwise, means a bulk energy storagesystem configured to may have a rated duration (energy/power ratio) of24 hours (h) or greater, such as a duration of 24 h, a duration of 24 hto 50 h, a duration of greater than 50 h, a duration of 24 h to 150 h, aduration of greater than 150 h, a duration of 24 h to 200 h, a durationgreater than 200 h, a duration of 24 h to 500 h, a duration greater than500 h, etc.

Example 1

A storage system, have from one, five, ten, 50, 100, 500, or moreelectrochemical cells, having an electrode or electrodes that includeconstitutes direct reduced iron pellets. Preferably the store system isa long duration storage system, having long duration electrochemicalcells.

Example 1A

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1A:

TABLE E1A Shape of pellets spheres Pellets having total Fe (wt %) 92Pellets having SiO₂ (wt %) 1.5 Pellets having Al₂O₃ (wt %) 0.2 Pelletshaving MgO (wt %) 0.1 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 80 Metallization (%) 94 Bulkdensity of the electrode (g/cc) 1.7 Apparent density of the pellets(g/cc) 3.5 Actual density of the pellets (g/cc) 6 Minimumd_(pore, 90% volume) of the pellets (microns) 0.966 Minimumd_(pore, 50% surface area) of the pellets 0.0114 (microns) Specificsurface area of the pellets (m²/g) 0.31

Example 1B

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1B:

TABLE E1B Shape of pellets beads Pellets having total Fe (wt %) 89Pellets having SiO₂ (wt %) 2 Pellets having Al₂O₃ (wt %) 0.3 Pelletshaving MgO (wt %) 0.1 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 15 Metallization (%) 94 Bulkdensity of the electrode (g/cc) 1.7 Apparent density of the pellets(g/cc) 3.5 Actual density of the pellets (g/cc) 6.1 Minimumd_(pore, 90% volume) of the pellets (microns) 4.53 Minimumd_(pore, 50% surface area) of the pellets 11.55 (microns) Specificsurface area of the pellets (m²/g) 0.69

Example 1C

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1C:

TABLE E1C Shape of pellets spheres Pellets having total Fe (wt %) 91Pellets having SiO₂ (wt %) 1 Pellets having Al₂O₃ (wt %) 0.5 Pelletshaving MgO (wt %) 0.1 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 0 Metallization (%) 94 Bulkdensity of the electrode (g/cc) 1.7 Apparent density of the pellets(g/cc) 3.3 Actual density of the pellets (g/cc) 5.9 Minimumd_(pore, 90% volume) of the pellets (microns) 4.4 Minimumd_(pore, 50% surface area) of the pellets 11.1 (microns) Specificsurface area of the pellets (m²/g) 0.74

Example 1D

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1D:

TABLE E1D Shape of pellets blocks Pellets having total Fe (wt %) 89Pellets having SiO₂ (wt %) 2 Pellets having Al₂O₃ (wt %) 0.5 Pelletshaving MgO (wt %) 0.1 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 15 Metallization (%) 94 Bulkdensity of the electrode (g/cc) 2.1 Apparent density of the pellets(g/cc) 3.6 Actual density of the pellets (g/cc) 6.2 Minimumd_(pore, 90% volume) of the pellets (microns) 4.2 Minimumd_(pore, 50% surface area) of the pellets 10.8 (microns) Specificsurface area of the pellets (m²/g) 0.72

Example 1E

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1E:

TABLE E1E Shape of pellets spheres Pellets having total Fe (wt %) 86Pellets having SiO₂ (wt %) 3 Pellets having Al₂O₃ (wt %) 3 Pelletshaving MgO (wt %) 0.75 Pellets having CaO (wt %) 1.5 Pellets having TiO₂(wt %) 0.75 Pellets having Fe₂C (wt %) 70 Metallization (%) 92 Bulkdensity of the electrode (g/cc) 1.5 Apparent density of the pellets(g/cc) 3.3 Actual density of the pellets (g/cc) 6.1 Minimumd_(pore, 90% volume) of the pellets (microns) 1.77 Minimumd_(pore, 50% surface area) of the pellets 0.15 (microns) Specificsurface area of the pellets (m²/g) 0.12

Example 1F

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1F:

TABLE E1F Shape of pellets columns Pellets having total Fe (wt %) 85Pellets having SiO₂ (wt %) 10 Pellets having Al₂O₃ (wt %) 1.5 Pelletshaving MgO (wt %) 0.1 Pellets having CaO (wt %) 1.5 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 3 Metallization (%) 92 Bulkdensity of the electrode (g/cc) 2 Apparent density of the pellets (g/cc)3.4 Actual density of the pellets (g/cc) 5.8 Minimumd_(pore, 90% volume) of the pellets (microns) 2.55 Minimumd_(pore, 50% surface area) of the pellets 1.74 (microns) Specificsurface area of the pellets (m²/g) 0.34

Example 1G

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1G:

TABLE E1G Shape of pellets spheres Pellets having total Fe (wt %) 84Pellets having SiO₂ (wt %) 6 Pellets having Al₂O₃ (wt %) 5 Pelletshaving MgO (wt %) 1 Pellets having CaO (wt %) 1.5 Pellets having TiO₂(wt %) 0.75 Pellets having Fe₂C (wt %) 5 Metallization (%) 92 Bulkdensity of the electrode (g/cc) 2 Apparent density of the pellets (g/cc)3.4 Actual density of the pellets (g/cc) 5.8 Minimumd_(pore, 90% volume) of the pellets (microns) 1.62 Minimumd_(pore, 50% surface area) of the pellets 0.57 (microns) Specificsurface area of the pellets (m²/g) 0.26

Example 1H

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1H:

TABLE E1H Shape of pellets spheres Pellets having total Fe (wt %) 84Pellets having SiO₂ (wt %) 2 Pellets having Al₂O₃ (wt %) 0.2 Pelletshaving MgO (wt %) 10 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 10 Metallization (%) 92 Bulkdensity of the electrode (g/cc) 2 Apparent density of the pellets (g/cc)3.4 Actual density of the pellets (g/cc) 5.8 Minimumd_(pore, 90% volume) of the pellets (microns) 1.27 Minimumd_(pore 50% surface area) of the pellets 0.42 (microns) Specific surfacearea of the pellets (m²/g) 0.41

Example 1I

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1I:

TABLE E1I Shape of pellets blocks Pellets having total Fe (wt %) 84Pellets having SiO₂ (wt %) 1.5 Pellets having Al₂O₃ (wt %) 2 Pelletshaving MgO (wt %) 0.1 Pellets having CaO (wt %) 10 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 2 Metallization (%) 92 Bulkdensity of the electrode (g/cc) 2 Apparent density of the pellets (g/cc)3.4 Actual density of the pellets (g/cc) 5.8 Minimumd_(pore, 90% volume) of the pellets (microns) 0.95 Minimumd_(pore, 50% surface area) of the pellets 0.78 (microns) Specificsurface area of the pellets (m²/g) 0.63

Example 1J

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1J:

TABLE E1J Shape of pellets disks Pellets having total Fe (wt %) 84Pellets having SiO₂ (wt %) 4 Pellets having Al₂O₃ (wt %) 1 Pelletshaving MgO (wt %) 0.5 Pellets having CaO (wt %) 1.5 Pellets having TiO₂(wt %) 5 Pellets having Fe₂C (wt %) 10 Metallization (%) 92 Bulk densityof the electrode (g/cc) 2 Apparent density of the pellets (g/cc) 3.4Actual density of the pellets (g/cc) 5.8 Minimum d_(pore, 90% volume) ofthe pellets (microns) 1.52 Minimum d_(pore, 50% surface area) of thepellets 2.82 (microns) Specific surface area of the pellets (m²/g) 0.51

Example 1K

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1K:

TABLE E1K Shape of pellets rods Pellets having total Fe (wt %) 84Pellets having SiO₂ (wt %) 5 Pellets having Al₂O₃ (wt %) 5 Pelletshaving MgO (wt %) 2 Pellets having CaO (wt %) 1 Pellets having TiO₂ (wt%) 1.5 Pellets having Fe₂C (wt %) 0 Metallization (%) 94 Bulk density ofthe electrode (g/cc) 1.8 Apparent density of the pellets (g/cc) 3.5Actual density of the pellets (g/cc) 6 Minimum d_(pore, 90% volume) ofthe pellets (microns) 2.72 Minimum d_(pore, 50% surface area) of thepellets 2.79 (microns) Specific surface area of the pellets (m²/g) 0.22

Example 1L

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1L:

TABLE E1L Shape of pellets Crushed spheres Pellets having total Fe (wt%) 85 Pellets having SiO₂ (wt %) 10 Pellets having Al₂O₃ (wt %) 0.2Pellets having MgO (wt %) 1.4 Pellets having CaO (wt %) 0.9 Pelletshaving TiO₂ (wt %) 0.05 Pellets having Fe₂C (wt %) 10 Metallization (%)92 Bulk density of the electrode (g/cc) 1.9 Apparent density of thepellets (g/cc) 3.4 Actual density of the pellets (g/cc) 6.1 Minimumd_(pore, 90% volume) of the pellets (microns) 3.26 Minimumd_(pore, 50% surface area) of the pellets 7.71 (microns) Specificsurface area of the pellets (m²/g) 0.11

Example 1M

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1M:

TABLE E1M Shape of pellets briquettes Pellets having total Fe (wt %) 91Pellets having SiO₂ (wt %) 3 Pellets having Al₂O₃ (wt %) 0.2 Pelletshaving MgO (wt %) 0.5 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 2.5 Metallization (%) 91 Bulkdensity of the electrode (g/cc) 3.3 Apparent density of the pellets(g/cc) 5.2 Actual density of the pellets (g/cc) 6.2 Minimumd_(pore, 90% volume) of the pellets (microns) 0.094 Minimumd_(pore, 50% surface area) of the pellets 0.0084 (microns) Specificsurface area of the pellets (m²/g) 0.024

Example 1N

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1N:

TABLE E1N Shape of pellets briquettes Pellets having total Fe (wt %) 86Pellets having SiO₂ (wt %) 9 Pellets having Al₂O₃ (wt %) 0.2 Pelletshaving MgO (wt %) 0.5 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 40 Metallization (%) 90 Bulkdensity of the electrode (g/cc) 2.5 Apparent density of the pellets(g/cc) 5 Actual density of the pellets (g/cc) 6.3 Minimumd_(pore, 90% volume) of the pellets (microns) 1.84 Minimumd_(pore, 50% surface area) of the pellets 0.0171 (microns) Specificsurface area of the pellets (m²/g) 0.015

Example 1O

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1O:

TABLE E1O Shape of pellets tubes Pellets having total Fe (wt %) 92Pellets having SiO₂ (wt %) 1.7 Pellets having Al₂O₃ (wt %) 0.2 Pelletshaving MgO (wt %) 0.5 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 50 Metallization (%) 94 Bulkdensity of the electrode (g/cc) 1.9 Apparent density of the pellets(g/cc) 3.9 Actual density of the pellets (g/cc) 6.2 Minimumd_(pore, 90% volume) of the pellets (microns) 0.096 Minimumd_(pore 50% surface area) of the pellets 0.0168 (microns) Specificsurface area of the pellets (m²/g) 0.035

Example 1P

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1P:

TABLE E1P Shape of pellets Strips Pellets having total Fe (wt %) 84Pellets having SiO₂ (wt %) 6 Pellets having Al₂O₃ (wt %) 3 Pelletshaving MgO (wt %) 0.5 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 10 Metallization (%) 90 Bulkdensity of the electrode (g/cc) 1.8 Apparent density of the pellets(g/cc) 3.9 Actual density of the pellets (g/cc) 6.1 Minimumd_(pore, 90% volume) of the pellets microns 1.98 Minimumd_(pore, 50% surface area) of the pellets 0.0123 (microns) Specificsurface area of the pellets (m²/g) 0.027

Example 1Q

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1Q:

TABLE E1Q Shape of pellets Powder Pellets having total Fe (wt %) 88Pellets having SiO₂ (wt %) 7 Pellets having Al₂O₃ (wt %) 2 Pelletshaving MgO (wt %) 0.5 Pellets having CaO (wt %) 0.9 Pellets having TiO₂(wt %) 0.05 Pellets having Fe₂C (wt %) 10 Metallization (%) 95 Bulkdensity of the electrode (g/cc) 3.5 Apparent density of the pellets(g/cc) 6.3 Actual density of the pellets (g/cc) 6.6 Minimumd_(pore, 90% volume) of the pellets (microns) 0.015 Minimumd_(pore 50% surface area) of the pellets 0.012 (microns) Specificsurface area of the pellets (m²/g) 1.21

Example 1R

The long duration storage system of Example 1, where the electrode hasthe properties shown in the following Table E1R:

TABLE E1R Shape of pellets spheres Pellets having total Fe (wt %) 80Pellets having SiO₂ (wt %) 4.9 Pellets having Al₂O₃ (wt %) 0.3 Pelletshaving MgO (wt %) 1.2 Pellets having CaO (wt %) 0.75 Pellets having TiO₂(wt %) 0.032 Pellets having Fe₂C (wt %) 5 Metallization (%) 60 Bulkdensity of the electrode (g/cc) 1.7 Apparent density of the pellets(g/cc) 5.1 Actual density of the pellets (g/cc) 5.4 Minimumd_(pore, 90% volume) of the pellets (microns) 0.0488 Minimumd_(pore, 50% surface area) of the pellets 0.0255 (microns) Specificsurface area of the pellets (m²/g) 24

Example 2

FIG. 15 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may beelectrically connected to a wind farm 1502 and one or more transmissionfacilities 1506. The wind farm 1502 may be electrically connected to thetransmission facilities 1506. The transmission facilities 1506 may beelectrically connected to the grid 1508. The wind farm 1502 may generatepower and the wind farm 1502 may output generated power to the LODESsystem 1504 and/or the transmission facilities 1506. The LODES system1504 may store power received from the wind farm 1502 and/or thetransmission facilities 1506. The LODES system 1504 may output storedpower to the transmission facilities 1506. The transmission facilities1506 may output power received from one or both of the wind farm 1502and LODES system 1504 to the grid 1508 and/or may receive power from thegrid 1508 and output that power to the LODES system 1504. Together thewind farm 1502, the LODES system 1504, and the transmission facilities1506 may constitute a power plant 1500 that may be a combined powergeneration, transmission, and storage system. The power generated by thewind farm 1502 may be directly fed to the grid 1508 through thetransmission facilities 1506, or may be first stored in the LODES system1504. In certain cases the power supplied to the grid 1508 may comeentirely from the wind farm 1502, entirely from the LODES system 1504,or from a combination of the wind farm 1502 and the LODES system 1504.The dispatch of power from the combined wind farm 1502 and LODES system1504 power plant 1500 may be controlled according to a determinedlong-range (multi-day or even multi-year) schedule, or may be controlledaccording to a day-ahead (24 hour advance notice) market, or may becontrolled according to an hour-ahead market, or may be controlled inresponse to real time pricing signals.

As one example of operation of the power plant 1500, the LODES system1504 may be used to reshape and “firm” the power produced by the windfarm 1502. In one such example, the wind farm 1502 may have a peakgeneration output (capacity) of 260 megawatts (MW) and a capacity factor(CF) of 41%. The LODES system 1504 may have a power rating (capacity) of106 MW, a rated duration (energy/power ratio) of 150 hours (h), and anenergy rating of 15,900 megawatt hours (MWh). In another such example,the wind farm 1502 may have a peak generation output (capacity) of 300MW and a capacity factor (CF) of 41%. The LODES system 1504 may have apower rating of 106 MW, a rated duration (energy/power ratio) of 200 hand an energy rating of 21,200 MWh. In another such example, the windfarm 1502 may have a peak generation output (capacity) of 176 MW and acapacity factor (CF) of 53%. The LODES system 1504 may have a powerrating (capacity) of 88 MW, a rated duration (energy/power ratio) of 150h and an energy rating of 13,200 MWh. In another such example, the windfarm 1502 may have a peak generation output (capacity) of 277 MW and acapacity factor (CF) of 41%. The LODES system 1504 may have a powerrating (capacity) of 97 MW, a rated duration (energy/power ratio) of 50h and an energy rating of 4,850 MWh. In another such example, the windfarm 1502 may have a peak generation output (capacity) of 315 MW and acapacity factor (CF) of 41%. The LODES system 1504 may have a powerrating (capacity) of 110 MW, a rated duration (energy/power ratio) of 25h and an energy rating of 2,750 MWh.

Example 2A

The System of Example 2 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 3

FIG. 16 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The system of FIG. 16 may besimilar to the system of FIG. 15 , except a photovoltaic (PV) farm 1602may be substituted for the wind farm 1502. The LODES system 1504 may beelectrically connected to the PV farm 1602 and one or more transmissionfacilities 1506. The PV farm 1602 may be electrically connected to thetransmission facilities 1506. The transmission facilities 1506 may beelectrically connected to the grid 1508. The PV farm 1602 may generatepower and the PV farm 1602 may output generated power to the LODESsystem 1504 and/or the transmission facilities 1506. The LODES system1504 may store power received from the PV farm 1602 and/or thetransmission facilities 1506. The LODES system 1504 may output storedpower to the transmission facilities 1506. The transmission facilities1506 may output power received from one or both of the PV farm 1602 andLODES system 1504 to the grid 1508 and/or may receive power from thegrid 1508 and output that power to the LODES system 1504. Together thePV farm 1602, the LODES system 1504, and the transmission facilities1506 may constitute a power plant 1600 that may be a combined powergeneration, transmission, and storage system. The power generated by thePV farm 1602 may be directly fed to the grid 1508 through thetransmission facilities 1506, or may be first stored in the LODES system1504. In certain cases the power supplied to the grid 1508 may comeentirely from the PV farm 1602, entirely from the LODES system 1504, orfrom a combination of the PV farm 1602 and the LODES system 1504. Thedispatch of power from the combined PV farm 1602 and LODES system 1504power plant 1600 may be controlled according to a determined long-range(multi-day or even multi-year) schedule, or may be controlled accordingto a day-ahead (24 hour advance notice) market, or may be controlledaccording to an hour-ahead market, or may be controlled in response toreal time pricing signals.

As one example of operation of the power plant 1600, the LODES system1504 may be used to reshape and “firm” the power produced by the PV farm1602. In one such example, the PV farm 1602 may have a peak generationoutput (capacity) of 490 MW and a capacity factor (CF) of 24%. The LODESsystem 1504 may have a power rating (capacity) of 340 MW, a ratedduration (energy/power ratio) of 150 h and an energy rating of 51,000MWh. In another such example, the PV farm 1602 may have a peakgeneration output (capacity) of 680 MW and a capacity factor (CF) of24%. The LODES system 1504 may have a power rating (capacity) of 410 MW,a rated duration (energy/power ratio) of 200 h, and an energy rating of82,000 MWh. In another such example, the PV farm 1602 may have a peakgeneration output (capacity) of 330 MW and a capacity factor (CF) of31%. The LODES system 1504 may have a power rating (capacity) of 215 MW,a rated duration (energy/power ratio) of 150 h, and an energy rating of32,250 MWh. In another such example, the PV farm 1602 may have a peakgeneration output (capacity) of 510 MW and a capacity factor (CF) of24%. The LODES system 1504 may have a power rating (capacity) of 380 MW,a rated duration (energy/power ratio) of 50 h, and an energy rating of19,000 MWh. In another such example, the PV farm 1602 may have a peakgeneration output (capacity) of 630 MW and a capacity factor (CF) of24%. The LODES system 1504 may have a power rating (capacity) of 380 MW,a rated duration (energy/power ratio) of 25 h, and an energy rating of9,500 MWh.

Example 3A

The System of Example 3 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 4

FIG. 17 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The system of FIG. 17 may besimilar to the systems of FIGS. 15 and 16 , except the wind farm ‘1502and the photovoltaic (PV) farm 1602 may both be power generators workingtogether in the power plant 1700. Together the PV farm 1602, wind farm1502, the LODES system 1504, and the transmission facilities 1506 mayconstitute the power plant 1700 that may be a combined power generation,transmission, and storage system. The power generated by the PV farm1602 and/or the wind farm 1502 may be directly fed to the grid 1508through the transmission facilities 1506, or may be first stored in theLODES system 1504. In certain cases the power supplied to the grid 1508may come entirely from the PV farm 1602, entirely from the wind farm1502, entirely from the LODES system 1504, or from a combination of thePV farm 1602, the wind farm 1502, and the LODES system 1504. Thedispatch of power from the combined wind farm 1502, PV farm 1602, andLODES system 1504 power plant 1700 may be controlled according to adetermined long-range (multi-day or even multi-year) schedule, or may becontrolled according to a day-ahead (24 hour advance notice) market, ormay be controlled according to an hour-ahead market, or may becontrolled in response to real time pricing signals.

As one example of operation of the power plant 1700, the LODES system1504 may be used to reshape and “firm” the power produced by the windfarm 1502 and the PV farm 1602. In one such example, the wind farm 1502may have a peak generation output (capacity) of 126 MW and a capacityfactor (CF) of 41% and the PV farm 1602 may have a peak generationoutput (capacity) of 126 MW and a capacity factor (CF) of 24%. The LODESsystem 1504 may have a power rating (capacity) of 63 MW, a ratedduration (energy/power ratio) of 150 h, and an energy rating of 9,450MWh. In another such example, the wind farm 1502 may have a peakgeneration output (capacity) of 170 MW and a capacity factor (CF) of 41%and the PV farm 1602 may have a peak generation output (capacity) of 110MW and a capacity factor (CF) of 24%. The LODES system 1504 may have apower rating (capacity) of 57 MW, a rated duration (energy/power ratio)of 200 h, and an energy rating of 11,400 MWh. In another such example,the wind farm 1502 may have a peak generation output (capacity) of 105MW and a capacity factor (CF) of 51% and the PV farm 1602 may have apeak generation output (capacity) of 70 MW and a capacity factor (CF) of31 The LODES system 1504 may have a power rating (capacity) of 61 MW, arated duration (energy/power ratio) of 150 h, and an energy rating of9,150 MWh. In another such example, the wind farm 1502 may have a peakgeneration output (capacity) of 135 MW and a capacity factor (CF) of 41%and the PV farm 1602 may have a peak generation output (capacity) of 90MW and a capacity factor (CF) of 24%. The LODES system 1504 may have apower rating (capacity) of 68 MW, a rated duration (energy/power ratio)of 50 h, and an energy rating of 3,400 MWh. In another such example, thewind farm 1502 may have a peak generation output (capacity) of 144 MWand a capacity factor (CF) of 41% and the PV farm 1602 may have a peakgeneration output (capacity) of 96 MW and a capacity factor (CF) of 24%.The LODES system 1504 may have a power rating (capacity) of 72 MW, arated duration (energy/power ratio) of 25 h, and an energy rating of1,800 MWh.

Example 4A

The System of Example 4 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 5

FIG. 18 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may beelectrically connected to one or more transmission facilities 1506. Inthis manner, the LODES system 1504 may operate in a “stand-alone” mannerto arbiter energy around market prices and/or to avoid transmissionconstraints. The LODES system 1504 may be electrically connected to oneor more transmission facilities 1506. The transmission facilities 1506may be electrically connected to the grid 1508. The LODES system 1504may store power received from the transmission facilities 1506. TheLODES system 1504 may output stored power to the transmission facilities1506. The transmission facilities 1506 may output power received fromthe LODES system 1504 to the grid 1508 and/or may receive power from thegrid 1508 and output that power to the LODES system 1504.

Together the LODES system 1504 and the transmission facilities 1506 mayconstitute a power plant 1800. As an example, the power plant 1800 maybe situated downstream of a transmission constraint, close to electricalconsumption. In such an example downstream situated power plant 1800,the LODES system 1504 may have a duration of 24 h to 500 h and mayundergo one or more full discharges a year to support peak electricalconsumptions at times when the transmission capacity is not sufficientto serve customers. Additionally, in such an example downstream situatedpower plant 1800, the LODES system 1504 may undergo several shallowdischarges (daily or at higher frequency) to arbiter the differencebetween nighttime and daytime electricity prices and reduce the overallcost of electrical service to customer. As a further example, the powerplant 1800 may be situated upstream of a transmission constraint, closeto electrical generation. In such an example upstream situated powerplant 1800, the LODES system 1504 may have a duration of 24 h to 500 hand may undergo one or more full charges a years to absorb excessgeneration at times when the transmission capacity is not sufficient todistribute the electricity to customers. Additionally, in such anexample upstream situated power plant 1800, the LODES system 1504 mayundergo several shallow charges and discharges (daily or at higherfrequency) to arbiter the difference between nighttime and daytimeelectricity prices and maximize the value of the output of thegeneration facilities.

Example 5A

The System of Example 5 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 6

FIG. 19 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may beelectrically connected to a commercial and industrial (C&I) customer1902, such as a data center, factory, etc. The LODES system 1504 may beelectrically connected to one or more transmission facilities 1506. Thetransmission facilities 1506 may be electrically connected to the grid1508. The transmission facilities 1506 may receive power from the grid1508 and output that power to the LODES system 1504. The LODES system1504 may store power received from the transmission facilities 1506. TheLODES system 1504 may output stored power to the C&I customer 1902. Inthis manner, the LODES system 1504 may operate to reshape electricitypurchased from the grid 1508 to match the consumption pattern of the C&Icustomer 1902.

Together, the LODES system 1504 and transmission facilities 1506 mayconstitute a power plant 1900. As an example, the power plant 1900 maybe situated close to electrical consumption, i.e., close to the C&Icustomer 1902, such as between the grid 1508 and the C&I customer 1902.In such an example, the LODES system 1504 may have a duration of 24 h to500 h and may buy electricity from the markets and thereby charge theLODES system 1504 at times when the electricity is cheaper. The LODESsystem 1504 may then discharge to provide the C&I customer 1902 withelectricity at times when the market price is expensive, thereforeoffsetting the market purchases of the C&I customer 1902. As analternative configuration, rather than being situated between the grid1508 and the C&I customer 1902, the power plant 1900 may be situatedbetween a renewable source, such as a PV farm, wind farm, etc., and thetransmission facilities 1506 may connect to the renewable source. Insuch an alternative example, the LODES system 1504 may have a durationof 24 h to 500 h, and the LODES system 1504 may charge at times whenrenewable output may be available. The LODES system 1504 may thendischarge to provide the C&I customer 1902 with renewable generatedelectricity so as to cover a portion, or the entirety, of the C&Icustomer 1902 electricity needs.

Example 6A

The System of Example 6 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 7

FIG. 20 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may beelectrically connected to a wind farm 1502 and one or more transmissionfacilities 1506. The wind farm 1502 may be electrically connected to thetransmission facilities 1506. The transmission facilities 1506 may beelectrically connected to a C&I customer 1902. The wind farm 1502 maygenerate power and the wind farm 1502 may output generated power to theLODES system 1504 and/or the transmission facilities 1506. The LODESsystem 1504 may store power received from the wind farm 1502. The LODESsystem 1504 may output stored power to the transmission facilities 1506.The transmission facilities 1506 may output power received from one orboth of the wind farm 1502 and LODES system 1504 to the C&I customer1902. Together the wind farm 1502, the LODES system 1504, and thetransmission facilities 1506 may constitute a power plant 2000 that maybe a combined power generation, transmission, and storage system. Thepower generated by the wind farm 1502 may be directly fed to the C&Icustomer 1902 through the transmission facilities 1506, or may be firststored in the LODES system 1504. In certain cases the power supplied tothe C&I customer 1902 may come entirely from the wind farm 1502,entirely from the LODES system 1504, or from a combination of the windfarm 1502 and the LODES system 1504. The LODES system 1504 may be usedto reshape the electricity generated by the wind farm 1502 to match theconsumption pattern of the C&I customer 1902. In one such example, theLODES system 1504 may have a duration of 24 h to 500 h and may chargewhen renewable generation by the wind farm 1502 exceeds the C&I customer1902 load. The LODES system 1504 may then discharge when renewablegeneration by the wind farm 1502 falls short of C&I customer 1902 loadso as to provide the C&I customer 1902 with a firm renewable profilethat offsets a fraction, or all of, the C&I customer 1902 electricalconsumption.

Example 7A

The System of Example 7 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 8

FIG. 21 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may be partof a power plant 2100 that is used to integrate large amounts ofrenewable generation in microgrids and harmonize the output of renewablegeneration by, for example a PV farm 1602 and wind farm 1502, withexisting thermal generation by, for example a thermal power plant 2102(e.g., a gas plant, a coal plant, a diesel generator set, etc., or acombination of thermal generation methods), while renewable generationand thermal generation supply the C&I customer 1902 load at highavailability. Microgrids, such as the microgrid constituted by the powerplant 2100 and the thermal power plant 2102, may provide availabilitythat is 90% or higher. The power generated by the PV farm 1602 and/orthe wind farm 1502 may be directly fed to the C&I customer 1902, or maybe first stored in the LODES system 1504. In certain cases the powersupplied to the C&I customer 1902 may come entirely from the PV farm1602, entirely from the wind farm 1502, entirely from the LODES system1504, entirely from the thermal power plant 2102, or from anycombination of the PV farm 1602, the wind farm 1502, the LODES system1504, and/or the thermal power plant 2102. As examples, the LODES system1502 of the power plant 2100 may have a duration of 24 h to 500 h. As aspecific example, the C&I customer 1902 load may have a peak of 100 MW,the LODES system 1504 may have a power rating of 14 MW and duration of150 h, natural gas may cost $6/million British thermal units (MMBTU),and the renewable penetration may be 58%. As another specific example,the C&I customer 1902 load may have a peak of 100 MW, the LODES system1504 may have a power rating of 25 MW and duration of 150 h, natural gasmay cost $8/MMBTU, and the renewable penetration may be 65%.

Example 8A

The System of Example 8 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 9

FIG. 22 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may be usedto augment a nuclear plant 2202 (or other inflexible generationfacility, such as a thermal, a biomass, etc., and/or any other typeplant having a ramp-rate lower than 50% of rated power in one hour and ahigh capacity factor of 80% or higher) to add flexibility to thecombined output of the power plant 2200 constituted by the combinedLODES system 1504 and nuclear plant 2202. The nuclear plant 2202 mayoperate at high capacity factor and at the highest efficiency point,while the LODES system 1504 may charge and discharge to effectivelyreshape the output of the nuclear plant 2202 to match a customerelectrical consumption and/or a market price of electricity. Asexamples, the LODES system 1502 of the power plant 2200 may have aduration of 24 h to 500 h. In one specific example, the nuclear plant2202 may have 1,000 MW of rated output and the nuclear plant 2202 may beforced into prolonged periods of minimum stable generation or evenshutdowns because of depressed market pricing of electricity. The LODESsystem 1502 may avoid facility shutdowns and charge at times ofdepressed market pricing; and the LODES system 1502 may subsequentlydischarge and boost total output generation at times of inflated marketpricing.

Example 9A

The System of Example 9 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 10

FIG. 23 illustrates an example system in which one or more aspects ofthe various embodiments may be used as part of bulk energy storagesystem. As a specific example, the bulk energy storage systemincorporating one or more aspects of the various embodiments may be aLODES system 1504. As an example, the LODES system 1504 may include anyof the various embodiment batteries and/or components described herein(e.g., any of batteries 100, 200, 400, 800, 814, 900, 1000, 1100, 1200,1300, 1310, pellets 105, 115, 305, 198, 199, systems 850, etc.),singularly or in various combinations. The LODES system 1504 may operatein tandem with a SDES system 2302. Together the LODES system 1504 andSDES system 2302 may constitute a power plant 2300. As an example, theLODES system 1504 and SDES system 2302 may be co-optimized whereby theLODES system 1504 may provide various services, including long-durationback-up and/or bridging through multi-day fluctuations (e.g., multi-dayfluctuations in market pricing, renewable generation, electricalconsumption, etc.), and the SDES system 2302 may provide variousservices, including fast ancillary services (e.g. voltage control,frequency regulation, etc.) and/or bridging through intra-dayfluctuations (e.g., intra-day fluctuations in market pricing, renewablegeneration, electrical consumption, etc.). The SDES system 2302 may havedurations of less than 10 hours and round-trip efficiencies of greaterthan 80%. The LODES system 1504 may have durations of 24 h to 500 h andround-trip efficiencies of greater than 40%. In one such example, theLODES system 1504 may have a duration of 150 hours and support customerelectrical consumption for up to a week of renewable under-generation.The LODES system 1504 may also support customer electrical consumptionduring intra-day under-generation events, augmenting the capabilities ofthe SDES system 2302. Further, the SDES system 2302 may supply customersduring intra-day under-generation events and provide power conditioningand quality services such as voltage control and frequency regulation.

Example 10A

The System of Example 10 where in the LODES system utilizes one or moreof the storage systems of Examples 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H,1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P, 1Q, and 1R.

Example 11

A non-limiting example according to embodiments of the invention wasbuilt and tested. An electrochemical cell using a direct reduced iron(DRI) pellet was assembled and tested. The DRI pellet had properties asoutlined in Table 4 as characterized according to the methods previouslydescribed. The electrochemical cell was a beaker-type cell with threeelectrodes (Working, Counter, and Reference) and was flooded with liquidelectrolyte. The electrolyte formulation was 5.5M KOH+0.5M LiOH+10 mMNa₂S. The counter electrode was a NiO/NiOOH electrode harvested from acommercial Fe/Ni (Edison-type) cell. The reference electrode was aHg/HgO (MMO) electrode, filled with 5.5 M KOH+0.5 M LiOH solution. Astainless steel hose clamp was used to make electrical contact to theDRI pellet. FIG. 24A shows the voltage of the DRI electrode vs. a MMOreference as a function of discharge specific capacity (mAh/g_(DRI))during the first electrochemical discharge cycle (oxidation of the DRI)when cycling at a 5 mA/g specific current.

TABLE 4 Shape of pellets spheres Pellets having total Fe (wt %) 88.6Pellets having SiO₂ (wt %) 6.1 Pellets having Al₂O₃ (wt %) 0.2 Pelletshaving MgO (wt %) 0.4 Pellets having CaO (wt %) 0.5 Pellets having TiO₂(wt %) 0.01 Pellets having Fe₂C (wt %) 0.2 Metallization (%) 89.4 Bulkdensity of the electrode (g/cc) 2.45 Apparent density of the pellets(g/cc) 6.35 Actual density of the pellets (g/cc) 6.54 Minimumd_(pore, 90% volume) of the pellets (microns) 2.72 Minimumd_(pore, 50% surface area) of the pellets 5 (microns) Specific surfacearea of the pellets (m²/g) 0.22

Example 12

Another non-limiting example according to embodiments of the inventionwas built and tested. A family of ten (10) electrochemical cells using adirect reduced iron (DRI) pellets were assembled and tested. The DRIpellets had properties as outlined in Table 4 as characterized accordingto the methods previously described. The electrochemical cells werebeaker-type cells with three electrodes (Working, Counter, andReference) and the cells were flooded with liquid electrolyte. Theelectrolyte formulation was 5.5 M KOH+0.5 M LiOH+10 mM Na₂S. The counterelectrode was a NiO/NiOOH electrode harvested from a commercial Fe/Ni(Edison-type) cell. The reference electrode was a Hg/HgO (MMO)electrode, filled with 5.5 M KOH+0.5 M LiOH solution. Stainless steelhose clamps were used to make electrical contact to the DRI pellets. TheDRI was electrochemically cycled according to the followingconditions: 1) Precharge at 25 mA/g specific current for 60 minutes; 2)Discharge at 25 mA/g specific current to 0 voltage vs. MMO; 3) Charge at25 mA/g specific current, terminating under a coulombic limitation, witha total charge equal to the first discharge capacity in mAh. FIG. 24B.shows the specific capacity of the DRI electrode (mAh/g_(DRI)) vs. cyclenumber for the family of cells. The mean capacity across all cells isplotted, along with error bars representing 95% confidence intervals.FIG. 24C shows the coulombic efficiency (CE) of the same DRI cells.

Example 13

In another non-limiting example, a bed of spherical DRI pellets wastested in beaker-type cell. The DRI pellet had properties as outlined inTable 4 as characterized according to the methods previously described.The pellet bed had a mass of 251.86 g. The electrolyte formulation was5.5 M KOH+0.5 M LiOH+60 mM Na₂S, and the volume of electrolyte used was348 mL. The counter electrode was a stainless steel mesh (100×100 mesh).A Hg/HgO (MMO) reference electrode with a 5.5 M KOH+0.5 M LiOH fillsolution was employed to measure anode potentials. A stainless steelperforated plate was used as a current collector for the DRI pellet bed,and a stainless steel slab was used as the counter electrode currentcollector. The cell utilized a 5 mA/g specific current for both chargingand discharging. FIG. 24D shows the voltage of the DRI electrode vs. aMMO reference as a function of discharge specific capacity(mAh/g_(DRI)).

The foregoing method descriptions are provided merely as illustrativeexamples and are not intended to require or imply that the steps of thevarious embodiments must be performed in the order presented. As will beappreciated by one of skill in the art the order of steps in theforegoing embodiments may be performed in any order. Words such as“thereafter,” “then,” “next,” etc. are not necessarily intended to limitthe order of the steps; these words may be used to guide the readerthrough the description of the methods. Further, any reference to claimelements in the singular, for example, using the articles “a,” “an” or“the” is not to be construed as limiting the element to the singular.Further, any step of any embodiment described herein can be used in anyother embodiment.

The preceding description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present invention.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of theinvention. Thus, the present invention is not intended to be limited tothe aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A battery, comprising: a first electrode; anelectrolyte; a second electrode, wherein one or both of the firstelectrode and the second electrode comprises direct reduced iron(“DRI”), wherein the DRI is in the form of pellets, and wherein thepellets have an average length ranging from about 10 mm to about 500 mm,an average width ranging from about 5 mm to about 250 mm, and an averageheight ranging from about 5 mm to about 200 mm; and a current collectorelectrically connected to the pellets.
 2. The battery of claim 1,wherein the pellets comprise at least about 60 wt % iron by elementalmass, based on the total mass of the pellets.
 3. The battery of claim 1,wherein the pellets comprise between about 90 wt % and about 98 wt %metallic iron, based on the total mass of the pellets.
 4. The battery ofclaim 1, wherein the pellets are spherical, rod-shaped, disk-shaped,plate shaped, briquette-shaped, or a combination thereof.
 5. The batteryof claim 4, wherein the pellets comprise hot briquetted iron formed frompowdered iron fines or iron pellets.
 6. The battery of claim 1, whereinthe DRI comprises iron ore, direct reduced grade iron ore, reducedtaconite, wustite, magnetite, hematite, cementite, iron oxide, or anycombination thereof.
 7. The battery of claim 1, wherein the DRIcomprises DRI fines or powder.
 8. The battery of claim 1, wherein thepellets have an average internal porosity ranging from about 10% toabout 90% by volume.
 9. The battery of claim 1, wherein the pellets havean average specific surface area ranging from about 0.19 m²/g to about18 m²/g.
 10. The battery of claim 1, wherein the pellets have a volumeweighted mean pore size ranging from 1 to 10 microns.
 11. The battery ofclaim 1, wherein at least one of the first electrode and the secondelectrode has a thickness of greater than 0.1 cm.
 12. The battery ofclaim 1, wherein the pellets are spherical and have an average diameterranging from about 0.5 mm to about 10 cm.
 13. The battery of claim 1,wherein the pellets comprise greater than 0.5 wt % percent silicacontaining compounds, based on the total weight of the pellets.
 14. Thebattery of claim 1, wherein the pellets comprise from about 1 wt % toabout 5 wt % silica containing compounds by elemental mass, based on thetotal mass of the pellets.
 15. The battery of claim 1, wherein thepellets comprise from about 1 wt % to about 25 wt % silica containingcompounds by elemental mass, based on the total mass of the pellets. 16.The battery of claim 1, wherein a packing fraction of the pellets in atleast one of the first electrode and the second electrode is between 30%and 74%.
 17. The battery of claim 1, wherein the pellets comprise: aprimary phase comprising iron; and a secondary phase comprising siliconor another metal.
 18. The battery of claim 1, wherein the pelletscomprise: a primary phase comprising iron; and a secondary phasecomprising cementite.
 19. The battery of claim 18, wherein the secondaryphase comprises silica or a silicate.
 20. The battery of claim 18,wherein the secondary phase comprises titanium, vanadium, manganese,magnesium, calcium, phosphorus, carbon, aluminum, zirconium, or anycombinations thereof.
 21. The battery of claim 1, wherein theelectrolyte is infiltrated between the pellets.
 22. The battery of claim1, wherein the current collector contacts a lower surface of at leastone of the first electrode and the second electrode, side surfaces of atleast one of at least one of the first electrode and the secondelectrode, extends through at least one of the first electrode and thesecond electrode, or any combination thereof.
 23. The battery of claim1, wherein the second electrode further comprises a slurry or a gel. 24.The battery of claim 1, wherein at least one of the first electrode andthe second electrode is a composite metal electrode comprising a mixtureof the pellets and a smaller metal particle composition.
 25. The batteryof claim 24, wherein the smaller metal particle composition is apowdered metal feedstock.
 26. The battery of claim 25, wherein powderedmetal feedstock is wetted by the electrolyte.
 27. The battery of claim24, wherein the smaller metal particle composition comprises DRI fines,sponge iron, atomized iron, or any combination thereof.
 28. The batteryof claim 27, wherein the pellets comprise DR taconite.
 29. The batteryof claim 1, wherein: the pellets are packed in a bed such thatmacro-pores are created between two or more pellets in contact with oneanother; and the pellets each include micro-pores in their respectiveouter surfaces.
 30. The battery of claim 29, wherein the pellets arefused together.
 31. The battery of claim 1, wherein the pellets arepre-processed chemically, mechanically, thermally, electrically, and/orelectrochemically to fuse at least a portion of the pellets into apacked bed.
 32. The battery of claim 1, wherein the pellets each includemicro-pores in their respective outer surfaces.
 33. The battery of claim1, wherein the pellets are initially comprised of at least a portion ofcementite (Fe₃C) before operation of the battery.
 34. The battery ofclaim 1, wherein at least one of the first electrode and the secondelectrode further comprises a layer of powdered iron configured to forman interface between the pellets and a current collector of the battery.35. The battery of claim 1, further comprising a monitoring systemconfigured to monitor the state-of-charge (SOC) and/or state-of-healthof at least one of the first electrode and the second electrode.
 36. Thebattery of claim 35, wherein the monitoring system comprises one or moresensor and the one or more sensor is selected from the group consistingof a strain gauge, a Mossbauer spectrometer, a CCD detector, anultrasonic transducer, an ion sensing electrode, a thermocouple, and agas sensor.
 37. The battery of claim 1, wherein at least one of thefirst electrode and the second electrode is a composite metal electrodecomprising a mixture of the pellets and a conductive material dispersedbetween individual ones of the pellets.
 38. The battery of claim 1,further comprising an additive delivery system configured to add one ormore additives to the electrolyte.
 39. The battery of claim 38, whereinthe one or more additives include a salt.
 40. The battery of claim 39,wherein the salt is a carbonate salt or polysulfide salt.
 41. Thebattery of claim 38, wherein the one or more additives include asulfur-based additive.
 42. The battery of claim 38, wherein the one ormore additives include a surfactant additive.
 43. The battery of claim38, wherein the one or more additives are configured to mitigateself-discharge and/or suppress the Hydrogen Evolution Reaction.
 44. Thebattery of claim 1, wherein at least one of the first electrode and thesecond electrode is under compressive force.
 45. The battery of claim 1,wherein at least one of the first electrode and the second electrodecomprises additional conductive material.
 46. The battery of claim 45,wherein the additional conductive material surrounds the iron-containingpellets.
 47. The battery of claim 45, wherein the additional conductivematerial is a foil, sheet, screen, or wire.
 48. A bulk energy storagesystem, comprising: one or more batteries, wherein at least one of theone or more batteries comprises: a first electrode; an electrolyte; asecond electrode, wherein one or both of the first electrode and thesecond electrode comprises direct reduced iron (“DRI”), wherein the DRIis in the form of pellets, and wherein the pellets have an averagelength ranging from about 10 mm to about 500 mm, an average widthranging from about 5 mm to about 250 mm, and an average height rangingfrom about 5 mm to about 200 mm; and a current collector electricallyconnected to the pellets.
 49. The bulk energy storage system of claim48, wherein at least one of the first electrode and the second electrodeis a negative electrode.
 50. The bulk energy storage system of claim 49,wherein at least one of the first electrode and the second electrodefurther comprises additive pellets.
 51. The bulk energy storage systemof claim 50, wherein the additive pellets are comprised of FeS, FeS₂,Na₂S, Bi₂O₃, a metal sulfide, or combinations thereof.
 52. The bulkenergy storage system of claim 48, wherein the pellets are sintered ironpellets comprised of crushed DRI precursors and/or DRI fines.
 53. Thebulk energy storage system of claim 48, wherein the pellets aremechanically, chemically, and/or thermally pre-processed beforeinstallation in at least one of the first electrode and the secondelectrode.
 54. The bulk energy storage system of claim 48, wherein thepellets comprise at least about 60 wt % metallic iron based on the totalmass of the pellets and the pellets comprise at least 60 percent of thetotal mass of at least one of the first electrode and the secondelectrode.
 55. The bulk energy storage system of claim 54, wherein thebulk energy storage system is a long duration energy storage (LODES)system.
 56. The bulk energy storage system of claim 53, wherein thepre-processing includes pre-charging the pellets.